I've been dogged by this message for months now, unable to update previously purchased apps to their newer version. After a bit of research this morning, I believe I've solved the issue. Hope this helps those out there with the same problem! Somewhere along the way, I changed my e-mail address AND my "apple ID" on iTunes to same. Since that time, any old apps that I had purchased and installed on the iPhone have received the error message when trying to update. What you need to do is to sign in to your "old" iTunes account (or possibly change the apple ID back to the old one) within iTunes, and then synch the iPhone again. Doing so will change your apple ID on the iPhone (temporarily) and allow you to update those old apps. When complete, don't forget to go back in and reset the login to your current one! Good luck!