(I can't leave a comment, apologies). I was getting this error running iOS 4.3.1 on iPad. I was compiling on the iPad itself, not running in the simulator. I tried everything - clean then rebuild, restarting XCode, deleting the app on iPad, running through the simulator then trying the iPad again.
What worked for me was deleting the app on my iPad, then XCode -> Product -> Clean, then rebooting the iPad (hold power button to switch off, then switch back on), then XCode -> Product Run. I don't know if all those steps are necessary, but I do know they worked! Thanks to tapdancemobile for the suggestion to restart iPad, just as you'd restart the simulator :)