i'll beat sub to the punch and suggest you post the tail end of your gbpvr.exe-native.log right after this happens (found in your GBPVR installation directory)...
I reverted my settings to the default, checked Use Live Preview Mode if Possible. But now, I can't pause live TV. Everytime I do, it will be thrown back to the main menu. This will happen even if I click record and only 2 sec or so of the show will record.