diff --git a/src/Mass/Mass.cpp b/src/Mass/Mass.cpp
index 84b6b45..7b81c68 100644
--- a/src/Mass/Mass.cpp
+++ b/src/Mass/Mass.cpp
@@ -35,8 +35,6 @@
 
 #include "Mass.h"
 
-std::string Mass::_lastError;
-
 Mass::Mass(const std::string& path) {
     _folder = Utility::Directory::path(path);
     _filename = Utility::Directory::filename(path);
@@ -50,28 +48,28 @@ auto Mass::lastError() -> std::string const& {
 
 auto Mass::getNameFromFile(const std::string& path) -> Containers::Optional<std::string> {
     if(!Utility::Directory::exists(path)) {
-        _lastError = path + " couldn't be found.";
+        Utility::Error{} << path.c_str() << "couldn't be found.";
         return Containers::NullOpt;
     }
 
     UESaveFile mass{path};
 
     if(!mass.valid()) {
-        _lastError = "The unit file seems to be corrupt.";
+        Utility::Error{} << "The unit file seems to be corrupt.";
         return Containers::NullOpt;
     }
 
     auto unit_data = mass.at<GenericStructProperty>("UnitData");
 
     if(!unit_data) {
-        _lastError = "Couldn't find unit data in the file.";
+        Utility::Error{} << "Couldn't find unit data in the file.";
         return Containers::NullOpt;
     }
 
     auto name_prop = unit_data->at<StringProperty>("Name_45_A037C5D54E53456407BDF091344529BB");
 
     if(!name_prop) {
-        _lastError = "Couldn't find the name in the file.";
+        Utility::Error{} << "Couldn't find the name in the file.";
         return Containers::NullOpt;
     }
 
@@ -378,7 +376,7 @@ auto Mass::writeJointSliders() -> bool {
     frame_prop->properties = std::move(temp);
 
     if(!_mass->saveToFile()) {
-        _lastError = "Couldn't write data to " + _filename;
+        _lastError = _mass->lastError();
         return false;
     }
 
@@ -445,7 +443,7 @@ auto Mass::writeFrameStyles() -> bool {
     }
 
     if(!_mass->saveToFile()) {
-        _lastError = "Couldn't write data to " + _filename;
+        _lastError = _mass->lastError();
         return false;
     }
 
@@ -482,18 +480,21 @@ auto Mass::writeEyeFlareColour() -> bool {
     auto unit_data = _mass->at<GenericStructProperty>("UnitData");
     if(!unit_data) {
         _state = State::Invalid;
+        _lastError = "No unit data in " + _filename;
         return false;
     }
 
     auto frame = unit_data->at<GenericStructProperty>("Frame_3_F92B0F6A44A15088AF7F41B9FF290653");
     if(!frame) {
         _state = State::Invalid;
+        _lastError = "No frame data in " + _filename;
         return false;
     }
 
     auto eye_flare_prop = frame->at<ColourStructProperty>("EyeFlareColor_36_AF79999C40FCA0E88A2F9A84488A38CA");
     if(!eye_flare_prop) {
         _state = State::Invalid;
+        _lastError = "No eye flare property in " + _filename;
         return false;
     }
 
@@ -502,7 +503,12 @@ auto Mass::writeEyeFlareColour() -> bool {
     eye_flare_prop->b = _frame.eyeFlare.b();
     eye_flare_prop->a = _frame.eyeFlare.a();
 
-    return _mass->saveToFile();
+    if(!_mass->saveToFile()) {
+        _lastError = _mass->lastError();
+        return false;
+    }
+
+    return true;
 }
 
 auto Mass::frameCustomStyles() -> Containers::ArrayView<CustomStyle> {
@@ -532,18 +538,21 @@ void Mass::getFrameCustomStyles() {
 
 auto Mass::writeFrameCustomStyle(UnsignedLong index) -> bool {
     if(index > _frame.customStyles.size()) {
+        _lastError = "Style index out of range.";
         return false;
     }
 
     auto unit_data = _mass->at<GenericStructProperty>("UnitData");
     if(!unit_data) {
         _state = State::Invalid;
+        _lastError = "No unit data in " + _filename;
         return false;
     }
 
     auto frame_styles = unit_data->at<ArrayProperty>("FrameStyle_44_04A44C9440363CCEC5443D98BFAF22AA");
     if(!frame_styles) {
         _state = State::Invalid;
+        _lastError = "No frame styles in " + _filename;
         return false;
     }
 
@@ -652,6 +661,14 @@ auto Mass::writeArmourPart(ArmourSlot slot) -> bool {
     }
 
     if(!part_prop) {
+        _lastError = "Couldn't find the armour part for slot ";
+        switch(slot) {
+            #define c(enumerator, strenum, name) case ArmourSlot::enumerator:                      \
+                                                     _lastError += "ArmourSlot::" #enumerator "."; \
+                                                     break;
+            #include "../Maps/ArmourSlots.hpp"
+            #undef c
+        }
         return false;
     }
 
@@ -670,7 +687,12 @@ auto Mass::writeArmourPart(ArmourSlot slot) -> bool {
         writeAccessories(part.accessories, accs_array);
     }
 
-    return _mass->saveToFile();
+    if(!_mass->saveToFile()) {
+        _lastError = _mass->lastError();
+        return false;
+    }
+
+    return true;
 }
 
 auto Mass::armourCustomStyles() -> Containers::ArrayView<CustomStyle> {
@@ -700,17 +722,20 @@ void Mass::getArmourCustomStyles() {
 
 auto Mass::writeArmourCustomStyle(UnsignedLong index) -> bool {
     if(index > _armour.customStyles.size()) {
+        _lastError = "Style index out of range.";
         return false;
     }
 
     auto unit_data = _mass->at<GenericStructProperty>("UnitData");
     if(!unit_data) {
         _state = State::Invalid;
+        _lastError = "Couldn't find unit data in " + _filename;
         return false;
     }
 
     auto armour_styles = unit_data->at<ArrayProperty>("ArmorStyle_42_E2F6AC3647788CB366BD469B3B7E899E");
     if(!armour_styles) {
+        _lastError = "Couldn't find armour custom styles in " + _filename;
         _state = State::Invalid;
         return false;
     }
@@ -817,18 +842,21 @@ void Mass::getGlobalStyles() {
 
 auto Mass::writeGlobalStyle(UnsignedLong index) -> bool {
     if(index > _globalStyles.size()) {
+        _lastError = "Global style index out of range";
         return false;
     }
 
     auto unit_data = _mass->at<GenericStructProperty>("UnitData");
     if(!unit_data) {
         _state = State::Invalid;
+        _lastError = "No unit data found in " + _filename;
         return false;
     }
 
     auto global_styles = unit_data->at<ArrayProperty>("GlobalStyles_57_6A681C114035241F7BDAAE9B43A8BF1B");
     if(!global_styles) {
         _state = State::Invalid;
+        _lastError = "No global styles found in " + _filename;
         return false;
     }
 
@@ -919,11 +947,17 @@ void Mass::getCustomStyles(Containers::ArrayView<CustomStyle> styles, ArrayPrope
 
 auto Mass::setCustomStyle(const CustomStyle& style, UnsignedLong index, ArrayProperty* style_array) -> bool {
     if(!style_array) {
+        _lastError = "Mass::setCustomStyle(): style_array is null.";
         return false;
     }
 
     auto style_prop = style_array->at<GenericStructProperty>(index);
 
+    if(!style_prop) {
+        _lastError = "Style index is out of range in " + _filename;
+        return false;
+    }
+
     style_prop->at<StringProperty>("Name_27_1532115A46EF2B2FA283908DF561A86B")->value = style.name;
     auto colour_prop = style_prop->at<ColourStructProperty>("Color_5_F0D383DF40474C9464AE48A0984A212E");
     colour_prop->r = style.colour.r();
@@ -940,7 +974,12 @@ auto Mass::setCustomStyle(const CustomStyle& style, UnsignedLong index, ArrayPro
     style_prop->at<FloatProperty>("Rotation_25_EC2DFAD84AD0A6BD3FA841ACD52EDD6D")->value = style.rotation;
     style_prop->at<FloatProperty>("Scale_26_19DF0708409262183E1247B317137671")->value = style.scale;
 
-    return _mass->saveToFile();
+    if(!_mass->saveToFile()) {
+        _lastError = _mass->lastError();
+        return false;
+    }
+
+    return true;
 }
 
 void Mass::getDecals(Containers::ArrayView<Decal> decals, ArrayProperty* decal_array) {
@@ -1162,17 +1201,20 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
     auto unit_data = _mass->at<GenericStructProperty>("UnitData");
     if(!unit_data) {
         _state = State::Invalid;
+        _lastError = "No unit data in " + _filename;
         return false;
     }
 
     auto prop = unit_data->at<ArrayProperty>(prop_name);
     if(!prop) {
         _state = State::Invalid;
+        _lastError = std::string{prop_name} + " not found in " + _filename;
         return false;
     }
 
     if(prop->items.size() != weapon_array.size()) {
         _state = State::Invalid;
+        _lastError = "Weapon type array size mismatch.";
         return false;
     }
 
@@ -1192,6 +1234,7 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
         auto parts_prop = weapon_prop->at<ArrayProperty>("Element_6_8E4617CC4B2C1F1490435599784EC6E0");
         if(parts_prop->items.size() != weapon.parts.size()) {
             _state = State::Invalid;
+            _lastError = "Weapon parts array size mismatch.";
             return false;
         }
 
@@ -1216,6 +1259,7 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
 
             if(part_accs->items.size() != part.accessories.size()) {
                 _state = State::Invalid;
+                _lastError = "Accessories array size mismatch.";
                 return false;
             }
 
@@ -1225,11 +1269,13 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
         auto custom_styles = weapon_prop->at<ArrayProperty>("Styles_10_8C3C82444B986AD7A99595AD4985912D");
         if(!custom_styles) {
             _state = State::Invalid;
+            _lastError = "No custom styles found for weapon.";
             return false;
         }
 
         if(custom_styles->items.size() != weapon.customStyles.size()) {
             _state = State::Invalid;
+            _lastError = "Custom styles array size mismatch.";
             return false;
         }
 
@@ -1243,7 +1289,7 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
             #include "../Maps/DamageTypes.hpp"
             #undef c
             default:
-                Utility::Warning{} << "Invalid damage type enum value in writeWeaponType().";
+                Utility::Warning{} << "Unknown damage type enum value in writeWeaponType().";
         }
         weapon_prop->at<BoolProperty>("DualWield_20_B2EB2CEA4A6A233DC7575996B6DD1222")->value = weapon.dualWield;
         switch(weapon.effectColourMode) {
@@ -1252,6 +1298,8 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
                                                break;
             #include "../Maps/EffectColourModes.hpp"
             #undef c
+            default:
+                Utility::Warning{} << "Unknown effect colour mode in writeWeaponType().";
         }
         auto effect_colour = weapon_prop->at<ColourStructProperty>("ColorEfx_26_D921B62946C493E487455A831F4520AC");
         effect_colour->r = weapon.effectColour.r();
@@ -1260,7 +1308,12 @@ auto Mass::writeWeaponType(const char* prop_name, Containers::ArrayView<Weapon>
         effect_colour->a = weapon.effectColour.a();
     }
 
-    return _mass->saveToFile();
+    if(!_mass->saveToFile()) {
+        _lastError = _mass->lastError();
+        return false;
+    }
+
+    return true;
 }
 
 void Mass::getTuningCategory(const char* big_node_prop_name, Int& big_node_id,
diff --git a/src/Mass/Mass.h b/src/Mass/Mass.h
index f46a4e9..3edfc3c 100644
--- a/src/Mass/Mass.h
+++ b/src/Mass/Mass.h
@@ -56,7 +56,7 @@ class Mass {
         Mass(Mass&&) = default;
         Mass& operator=(Mass&&) = default;
 
-        static auto lastError() -> std::string const&;
+        auto lastError() -> std::string const&;
 
         static auto getNameFromFile(const std::string& path) -> Containers::Optional<std::string>;
 
@@ -156,7 +156,7 @@ class Mass {
 
         Containers::Optional<UESaveFile> _mass;
 
-        static std::string _lastError;
+        std::string _lastError;
 
         std::string _folder;
         std::string _filename;
diff --git a/src/SaveTool/SaveTool_MassViewer.cpp b/src/SaveTool/SaveTool_MassViewer.cpp
index 2bd8730..b19ba9b 100644
--- a/src/SaveTool/SaveTool_MassViewer.cpp
+++ b/src/SaveTool/SaveTool_MassViewer.cpp
@@ -319,7 +319,7 @@ void SaveTool::drawJointSliders() {
     else {
         if(drawUnsafeWidget([]{ return ImGui::Button(ICON_FA_SAVE " Save"); })) {
             if(!_currentMass->writeJointSliders()) {
-                _queue.addToast(Toast::Type::Error, "Error: " + Mass::lastError());
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
             }
             _jointsDirty = false;
         }
@@ -368,7 +368,7 @@ void SaveTool::drawFrameStyles() {
     else {
         if(drawUnsafeWidget([]{ return ImGui::Button(ICON_FA_SAVE " Save"); })) {
             if(!_currentMass->writeFrameStyles()) {
-                _queue.addToast(Toast::Type::Error, "Error: " + Mass::lastError());
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
             }
             _stylesDirty = false;
         }
@@ -399,7 +399,7 @@ void SaveTool::drawEyeColourPicker() {
     else {
         if(drawUnsafeWidget([]{ return ImGui::Button(ICON_FA_SAVE " Save"); })) {
             if(!_currentMass->writeEyeFlareColour()) {
-                _queue.addToast(Toast::Type::Error, "Error writing the eye flare colour.");
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
             }
             _eyeFlareDirty = false;
         }
@@ -432,7 +432,9 @@ void SaveTool::drawCustomFrameStyles() {
                 _currentMass->getFrameCustomStyles();
                 break;
             case DCS_Save:
-                _currentMass->writeFrameCustomStyle(i);
+                if(!_currentMass->writeFrameCustomStyle(i)) {
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+                }
                 break;
             default:
                 break;
@@ -576,7 +578,9 @@ void SaveTool::drawArmour() {
             ImGui::Separator();
 
             if(drawUnsafeWidget([]{ return ImGui::Button(ICON_FA_SAVE " Save"); })) {
-                _currentMass->writeArmourPart(part.slot);
+                if(!_currentMass->writeArmourPart(part.slot)) {
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+                }
             }
         }
 
@@ -607,7 +611,9 @@ void SaveTool::drawCustomArmourStyles() {
                 _currentMass->getArmourCustomStyles();
                 break;
             case DCS_Save:
-                _currentMass->writeArmourCustomStyle(i);
+                if(_currentMass->writeArmourCustomStyle(i)) {
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+                }
                 break;
             default:
                 break;
@@ -713,28 +719,57 @@ void SaveTool::drawWeapons() {
 
     if(drawUnsafeWidget([]{ return ImGui::Button(ICON_FA_SAVE " Save"); })) {
         if(_meleeDirty) {
-            _currentMass->writeMeleeWeapons();
-            _meleeDirty = false;
+            if(!_currentMass->writeMeleeWeapons()) {
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+            }
+            else {
+                _meleeDirty = false;
+            }
         }
+
         if(_shieldsDirty) {
-            _currentMass->writeShields();
-            _shieldsDirty = false;
+            if(!_currentMass->writeShields()) {
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+            }
+            else {
+                _shieldsDirty = false;
+            }
         }
+
         if(_bShootersDirty) {
-            _currentMass->writeBulletShooters();
-            _bShootersDirty = false;
+            if(!_currentMass->writeBulletShooters()) {
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+            }
+            else {
+                _bShootersDirty = false;
+            }
         }
+
         if(_eShootersDirty) {
-            _currentMass->writeEnergyShooters();
-            _eShootersDirty = false;
+            if(_currentMass->writeEnergyShooters()) {
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+            }
+            else {
+                _eShootersDirty = false;
+            }
         }
+
         if(_bLaunchersDirty) {
-            _currentMass->writeBulletLaunchers();
-            _bLaunchersDirty = false;
+            if(_currentMass->writeBulletLaunchers()) {
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+            }
+            else {
+                _bLaunchersDirty = false;
+            }
         }
+
         if(_eLaunchersDirty) {
-            _currentMass->writeEnergyLaunchers();
-            _eLaunchersDirty = false;
+            if(_currentMass->writeEnergyLaunchers()) {
+                _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+            }
+            else {
+                _eLaunchersDirty = false;
+            }
         }
     }
 
@@ -797,32 +832,32 @@ void SaveTool::drawWeapons() {
         switch(current_weapon->type) {
             case WeaponType::Melee:
                 if(!_currentMass->writeMeleeWeapons()) {
-                    _queue.addToast(Toast::Type::Error, "Couldn't save melee weapons");
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
                 }
                 break;
             case WeaponType::Shield:
                 if(!_currentMass->writeShields()) {
-                    _queue.addToast(Toast::Type::Error, "Couldn't save shields");
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
                 }
                 break;
             case WeaponType::BulletShooter:
                 if(!_currentMass->writeBulletShooters()) {
-                    _queue.addToast(Toast::Type::Error, "Couldn't save bullet shooters");
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
                 }
                 break;
             case WeaponType::EnergyShooter:
                 if(!_currentMass->writeEnergyShooters()) {
-                    _queue.addToast(Toast::Type::Error, "Couldn't save energy shooters");
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
                 }
                 break;
             case WeaponType::BulletLauncher:
                 if(!_currentMass->writeBulletLaunchers()) {
-                    _queue.addToast(Toast::Type::Error, "Couldn't save bullet launchers");
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
                 }
                 break;
             case WeaponType::EnergyLauncher:
                 if(!_currentMass->writeEnergyLaunchers()) {
-                    _queue.addToast(Toast::Type::Error, "Couldn't save energy launchers");
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
                 }
                 break;
             default:
@@ -1068,7 +1103,9 @@ void SaveTool::drawGlobalStyles() {
                 _currentMass->getGlobalStyles();
                 break;
             case DCS_Save:
-                _currentMass->writeGlobalStyle(i);
+                if(!_currentMass->writeGlobalStyle(i)) {
+                    _queue.addToast(Toast::Type::Error, _currentMass->lastError());
+                }
                 break;
             default:
                 break;