Given that I no longer own a Canon DSLR and this post has gotten much too much attention, I refer you to a better source of information on this electrical problem with Canon DSLR bodies and/or lenses that have dirty or off spec electrical contacts:
This post had over 4000 comments on it starting in 2005 and running all the way up through July of this year (2013). I decided that it was about time to retire the cumbersome comment thread and the post as it was.
I’m leaving the comments up for now but am turning off the ability to make new ones. I can’t be much help anymore anyway, my job is long done.
I’ll be deleting this comment thread at some point in the next year or so.