This is a pre-solved problem, but in case anyone else has it…
I was trying to open my project as usual – after having deleted some libraries – and Unity was failing silently… I’d hit “Open Project” and nothing would happen. I checked the log file (at ${USER}\AppData\Local\Unity\Editor\Editor.log in Windows) and noticed a lot of the following type of error:
TypeLoadException: Could not load type 'UnityEngine.Vector3'
…which seemed odd, since that’s a very basic class. As far as I can tell, though, it was the fact that I deleted those other libraries that caused the problem.
I went into ${PROJECT}\Library\ScriptAssemblies and deleted all the files there; the next time I opened Unity, it recompiled all my scripts, and the project opened just fine.
Hope this helps.
