сцуко!!!!

When Canon first cooked up the EOS system and then moved to the EOS digital system, they had to think up some error codes to display. They expected a few and documented them as Err 1, Err 2, etc. Then, as an afterthought, they figured that Err 99 would be a good catch-all for anything else. In some cases, Err 99 means that something wrong happened, but then it cleared out before it could be further determined.

When the communications between the camera body and the lens would have some non-Canon message pop in there, the body will display Err 99. There are other diverse reasons for Err 99, but lens-to-body problems are common.