Trashing prefs is step #1 for odd behavior(and this sounds odd to me). In fact, I would uninstall Pro Tools(and prefs) and reinstall
You will need to reset your preferences, but you need to try that anyway(somewhere on the DUC, you should be able to find a link to the Pete Gates utility for Mac users)
I would also double-check the compatibility chart(see
Help Us Help You near the top) and make sure you are running the correct version of PT for your version of OS.