Ipod

I recently had my iPhone replaced as the first one was faulty. Now after having the new one for a week or so and after syncing it a number of times with my Intel Core Duo 2 21"iMac I am getting USB over current notice whenever I attach the ipHone to my iMac and it doesn’t sync. I have tried attaching it via a USB hub and I still get the same error. Can anyone advise me of what may have caused this and a possible way around ti?