I have iPad 1, IOS 4.3.3 and iTunes for Windows. When I try to sync it gets to about 90% of backing up and just hangs. If I use the slider on the iPad to stop the sync, iTunes still thinks it's connected. I then physically remove the iPad and iTunes recognises the disconnect. i then reconnect and it goes straight to step 2. At the end of that, I get a message "iTunes could not backup the iPad because a sessions could not be started with the iPad". Then another message "iTunes could not sync inforation to the iPad because another sunc sessions was already running".
Shortly after this fiasco the iPad may hang to the apple logo and require a cold boot.