The Canon EOS and Digital Rebel Err 99 error message has been plaguing EOS DSLR camera users for quite a long time now. There's this understanding that Canon knows what the difficulty is and is lying to consumers about the actual meaning of the error message. Here's the genuine answer, and it is not about to make you happy, sorry.
Err 99 is a common error message on Canon EOS digital cameras that means there's some sort of bad thing happening but the camera isn't sure exactly what! Error 99 is not a particular error code that may be used to indicate an actual problem or a design failing with the camera!
For example, these are error messages from page 171 of the Canon EOS 10D manual :
Err 01 - Clean the lens contacts
Err 02 - There's a issue with the CF card...
Err 04 - The CF Card is full...
Err 05 - Something is obstructing the built in flash....
Err 99 - An error aside from the above...
It's the same as the old Canon E:18 error message that simply means there's a problem with the lens. Thousands of people went off the deep end with this code and thought it meant it had been a lens design flaw and Canon knew all about it. Canon subsequently dropped the E:18 error code in favor of "Lens error, restart camera" and similar codes instead.
If you have any DSLR camera you may at some specific point in time ; if you use the camera enough, a failure of the shutter box assembly. This is to all intents and purposes the only moving part of the camera and so it will one day wear out and break.
Canon entry level Digital Rebel cameras have less robust shutter box assemblies than their pro counterparts, and can wear out after 10-15,000 shots. If you take a lot of shots this might only last you a few years. A Canon EOS pro DSLR has a shutter box rated as high as two hundred to three hundred thousand shots which would probably last the average consumer their entire lifetime.
If a professional photographer has an Err 99 display on one of his or her cameras, they understand their shutter box is at the end of its lifespan because of normal useage; they do not blame Canon. Why is it that when shoppers see this error message they blame Canon and desire to get paid? Cant we acknowledge that the moving part of the camera has a limited lifespan and will one day need to be replaced? Do we blame an automobile manufacturer when things break on our automobiles? No, we just pay hundreds or perhaps thousands to have it fixed.
If you have a Canon EOS DSLR with the Err 99 flaw there are numerous things you can attempt first before paying for Canon Err 99 repair to have it fixed. You should try cleaning the lens and body contact points with a pencil eraser, and you can try putting in a new memory card. If these things dont work you probably do need to start looking for Canon EOS Error 99 repair. It's not a design issue, its just ordinary wear from use.