Visual Studio Error: The "Microsoft.VisualStudio.Editor.Implementation.EditorPackage" package did not load correctly

Have you tried to remove %LOCALAPPDATA%\Microsoft\VisualStudio\11.0\ComponentModelCache and restarting VS2012 / VS2013 may fix the problem

With VS2019 I had to:

1. Remove all contents of C:\Users\{your_username}\AppData\Roaming\Microsoft\VisualStudio\*
2. Remove C:\Users\{your_username}\AppData\Local\Microsoft\VisualStudio\16.0_xxxx\ComponentModelCache
3. Restart Visual Studio as Admin, otherwise the folders weren't being recreated/repaired by Visual Studio.