Recently, when I attempted to sync my iPad in iTunes, the following message popped up near the end of the sequence of steps:
After clicking OK, a second related message immediately followed:
You won’t be surprised to learn that the backup indeed failed, although the rest of the sync proceeded normally.
I had occasionally gotten these messages on previous occasions. Typically, the cause was precisely what the second message suggested: Another open application was grabbing the iPad’s attention. Apparently, iTunes doesn’t like to share. In my case, the competing program was Ecamm Network’s PhoneView. If I quit PhoneView, the syncing problem in iTunes would vanish. Despite this, PhoneView and iTunes would sometimes get along fine, with no unruly error messages even when they were both open.
On this occasion, however, the iTunes error messages appeared even though PhoneView was nowhere in sight. As far as I could tell, no other iOS-related app was open. What had happened is that, on my immediately prior sync attempt, iTunes stalled at the “Backing up” step. After waiting several minutes, I decided that it was never going to finish. I clicked iTunes' X button to cancel the sync. It had no effect. I ultimately had to force quit iTunes. When I relaunched iTunes and tried to sync again, the above-cited error messages showed up.
Figuring that the iPad’s backup file might be corrupt, I went to the Devices section of iTunes Preferences and selected to delete the backup. I next restarted the Mac. No dice. The sync error persisted.
Finally, I turned my attention to the iPad itself: I selected to power down and restart the iPad. I had some unexpected difficulty here as well; I needed to do a forced restart (holding down the Sleep/Wake and Home buttons simultaneously for around 10 seconds) before I could get the iPad to progress to the Lock screen.
The good news is that this did the trick. When I next went to iTunes, the iPad backed up and synced without a hitch. Numerous users have reported the same “dreaded ‘session could not be started’ syncing problem” and most have had similar success after an iPad restart.
All has proceeded normally on subsequent sync attempts. I’m still not sure precisely what precipitated the problem, but at least I now know how to fix it.