I can't speak for the OP, but I've just now encountered the same problem with the whole library (the pane/window is just a white space), and nothing suggested here worked for me.  I also tried re-installing PP12.  Still nothing.  I'm suspicious it has something to do with Norton 360, since the problem started after my first re-boot since installing it, but setting my Firewall settings to "Allow"for PP12 didn't help either.  The setting is already "Allow" for Flash Player 11.  Does anyone have any more suggestions?

Thanks in advance!