RE: GP Add In : Designer Error on WinForms.Controls
I have recently found out more information about this error. Even so it still seems slightly mysterious.
There are posts about this issue that will state a serious of solution cleans and rebuilds will resolve the problem. Not so for me.
From J Collins' answer to this post at stackoverflow, I found that libraries are copied to dynamically created folders when a project is loaded. I'm using VS 2012 so my location was :
C:\Users\[user_name]\AppData\Local\Microsoft\VisualStudio\11.0\ProjectAssemblies
In my broken project only the Dexterity.Shell library was copied to this location. I had found another post where a person stated that creating a traditional reference to their problem library resolved the issue - and mysteriously if he then removed that reference the project continued to work. I have not tested removal of my reference, but creating the traditional reference to the Winforms.Controls library did resolve my problem. Also, the library is being copied to the Project Assemblies folder when the project loads.
Interestingly, my first project that broke is now opening the designer successfully as well even though I have not created a traditional reference to the library. Hence the exact problem is still a bit blurry.