I apologize if I came off condescending. It is no excuse, but there are a lot of instances of not RTFM. Obviously your not one of these instances.
Back to the tech rudeness 
Do you have the current fuse settings of the 16u2? Does AVRDUDE or AVR ONE! read anything from the 16u2 chip (SIG, etc)?
While I have yet to have an issue with the 8u2/16u2, I shall tear into one of them and share your pain.
Check back tomorrow for my Arduino cursing