What camera do you have? What lens is on it when you get this error?
I have an eos 300d and standard canon 28-90 lens. It has worked flawlessly for years, this year I took it to japan and the cold temps were causing it to malfunction badly. To use it I would have to take the lens off and the battery out, warm the contacts with my fingers (as my fingers froze), reinstall and quickly shoot before it happened again. Get back to the warm room and it wont do it. I am not trying to scare you off but this IS a real problem with canon cameras, like I said do a google search and see the thousands of topics regarding it.