I just got this error with latest Playmaker & latest ProBuilder, ProGrids.
(Playmaker 1.7.7f6, ProBuilder 2.2.5f5 v2341, ProGrids 2.1.3 v2464)
and solved this problem with renaming(refactoring) some classnames on Playmaker itself.
At first, I examined all sources and found it's not caused by them.
All of their ProCore window sources is already started with 'pc_'...
and when I caught by this error, the corresponding Playmaker source -
Playmaker/Editor/AboutWindow.cs was strangely disappeared.
- - - - -
Well then,
First I made a clean project and installed Playmaker only.
Then I just temporarily renamed some 'too familiar' classnames
that cause conflict now, like :
(Actually, It's a refactoring in MonoDevelop.
It renames not only the classname itself, but all of references and class filenames.)
AboutWindow -> plmk_AboutWindow
ContextToolWindow -> plmk_ContextToolWindow
ReportWindow -> plmk_ReportWindow
(I think this prefix is better with 'PlayMaker...' or something,
however I'll leave it to Hutong.)
Finally, I imported all the ProCore assets i need. (ProBuilder, ProGrid, etc.)
It works well, and I'm using all of that with no errors.
Hope this helps.
ps:
Dear Hutong,
Please refactor all that 'general, familiar classnames' at next release
to avoid future conflicts...
Thanks in advance! ;-)