Reading http://photography-on-the.net/forum/showthread.php?t=425474 tells me 2 new things.
1. That other battery.
2. That issue with some lenses.
Sorry but I can't tell if that helps as some have only one lens.
I have tried the recommended fix -- clean all contacts; lens to body, battery to body, remove & replace battery, even purchased a brand new battery. At one point, I even did a complete re-set but nothing has worked so far.
The Canon camera store in OKC said they could fix the problem -- but didn't tell me how -- and told me it would cost $250. I am not believing that; the camera is only 4 years old and I haven't used it that much. PLEASE HELP!