Recently both my new iPad and iPhone4 stopped syncing with the iTunes on my Mac Mini. Plug the device in to the computer, and a couple moments later this message pops up: "the ipad could not be synced because the sync session failed to start". I tried several things at random, nothing worked. I yahoogled the phrase and found some complex discussion on the Apple Support discussion boards. For example, this problem existed for Mac OS X 10.5b1. In my case I'm on Mac OS X 10.7.3 and iTunes 10.6, so that wasn't the culprit. Other suggestions talked about doing a hard reset on the device, or a restore of the device. Someone talked of having gone to the Guru's at the Apple store, and not get any satisfaction.
My solution? I didn't want to do anything drastic.
I quit iTunes .. then plugged the device into the Mac. This restarted iTunes automatically, and then the sync started right up.
Whew, way simple.