Bugs? GetPersistentManager

I was also getting the former error (4.3.0f4, OS X).

Trashed everything in my project folder that isn't checked in (`*.csproj`, *.unityproj, *.sln, *.user, and *.userprefs files, and the Library dir) and it went away.  Make sure you have Visible Meta Files turned on in the Editor Settings before you do this.

This kind of thing happens from time-to-time— especially if you're writing editor scripts.  Unity's intermediate state serialization becomes corrupt and rebuilding from the assets and meta files fixes it.  Since the above is a heavy-handed approach, you may want to try running Assets▸Reimport All first.

I'm sure this is covered somewhere in the official Unity docs, and said coverage may provide a recommended alternative to my given solution(s).  I'm just going on memory/experience here.