Recently I upgraded my iPhone 3Gs to iOS 4.0 and came accross a problem. I chose to upgrade my software rather than do a full restore, but when trying to sync my iPhone with iTunes 9.2 (required for the new iOS) I get the following error message.
iTunes could not back up the iphone … because a session could not be started with the iPhone.
It seems as though iTunes will not backup my iPhone nor can it restore from a backup. I can install or remove apps, and move media on and off the iPhone with iTunes and there seems to be no problems other than the backups.
I searched through the apple discussion boards and Google, and found lots of suggestions but no working solution.
I also tried an inplace upgrade of the software over top of the current installation but that did not change the situation.
I finally had to do a factory restore. Because I had backed up my iPhone before this whole process, once I performed the restore, I was then able to restore my iPhone from its backup. Then I went through the process of setting up all of the new iPhone 4 settings and preferences which were not in the backup. This also meant reinstalling all of the applications as well.
Everything is working fine now and what did I learn from this, backups are valueable so take the time to do them.