Just a quick note to observe the simple solution to the "Err 99" message occasionally obtained with numerous Canon digital cameras - whilst this is not necessarily the cause, frequently, the problem is that the gold contacts are dirty. Solution? Easy: erase them. With a standard pencil eraser. At your own risk!
Other techniques which can work (i.e. try at your own peril) include:
- Re-inserting the CF card
- Re-inserting the battery pack
- Re-aligning the shutter curtain (lift mirror and brush lightly into place)
- Being careful about switching the camera off before changing lenses etc.
- Letting battery go flat whilst exposed (?!)
Worked for me!