[Andrew]

Is it possible that your phone configuration has gotten confused such that it no longer realizes it's supposed to be associated with your app store account?

Otherwise, if you have your OmniFocus database synced to a network server or to a desktop copy of OmniFocus, you might try deleting and reinstalling OmniFocus on the phone (make sure you do a sync right beforehand to be sure all of your data is preserved, as deleting it will also destroy the local copy of your data). I would expect that to get the most current version of the application.