Quite a few readers have been having issues with Kobo reader in the last few weeks and we knew Kobo was working on it. Scuebydue pointed out in the forums that the eBooks by Kobo app for the PlayBook has been updated to v1.3.1 this week. This version is supposed to fix many of those problems so it is definitely worth a shot. I was hoping it would also allow you to sideload your own books but that does not seem to be the case.
Either way you can pick up the updated eBooks by Kobo app in App World free