mk9906 wrote:
I put the passcode on it *after* the September update so I guess I haven't synched since then.
That explains why you can't restore from backup to remove it. After you first passcode protect your phone & then connect to iTunes to sync or restore, you'll be prompted to input your passcode. After that initial prompt, you won't be prompted again. Unfortunately, Apple won't be able to help you and if you can't remember the passcode(I know you keep saying you're entering it correctly), your only choice now is to restore your phone as a new device in iTunes. This will remove the passcode, but erase all data on your phone. If the erased data is on your computer, you can sync it back or restore from a previous backup after you restore as new. If you go to an Apple store, if they do anything, it will be to restore your phone as a new device.