I think their is something up with iTunes 10.5.1.42. I updated to that version and both my iPad 1 (4.3.3) and my wifes Iphone 4s (5.0) would fail at back up. I tried everything that I could think of and nothing worked. So I reverted back to the last version that worked 10.2.2.12. Now I am running without any issues and backup is working fine for my iPad.
However, I cannot backup the wifes iPhone4s since it requires the newest version of iTunes. Can someone think of anything that I can do? It must be a conflict with something on my machine and iTunes 10.5.1.42, but how could I go about finding that conflict. I rather have both devices be linked.