[Darryl Ramm]

My impression is too often people leap to reinstall Pro Tools and it often does not help. You've trashed prefs but have you tried any other possible troubleshooting?

Make sure you are fully trashing prefs correctly for your Pro Tools and OS X version. Best to use the PT Preds utility.

This only happen in one session? Tried a Save Session In... or create new session and import into to look for a corrupted session (not exactly an uncommon problem). When did this start? Can you roll back to an older session?

Remove plugin files from the plugin folder, trash prefs, and put them back in batches looking for problems. Any new plugins added/updated recently? All plugin versions claimed to be compatible with your OS and Pro Tools version?

Try creating a new admin account and testing from there.

If after trying all that, and you still have problems then I'd consider reinstalling Pro Tools, and if still having problems not waste too much time before considering doing a full clean OS X install.