Jack, first off [http://www.lensrentals.com/blog/2008/12/canons-error-99-the-man-the-myth|here is] some great general information about the error. Since your got the error after a fall, I would check the lens itself. The error may originate by a lens-body failure to communicate. Remove the lens and clean the contacts with an eraser and replace it . See what happens. Here is another great way to trouble shot " To isolate the cause of the issue, we suggest that you do the following:
1. Turn off the camera.
2. Remove the lens, battery, and CF card.
3. Allow the camera to sit without power for approximately 20 minutes.
4. Insert a fully charged battery, and turn on the camera.
5. Depress the shutter button as you would to take a picture.
Does the “ERR 99″ message appear? If it does, then the camera should be
serviced. If it does not, then please proceed to the next set of steps:
1. Turn off the camera.
2. Insert the CF card.
3. Turn on the camera.
4. Format the CF card in the camera.
5. Depress the shutter button as you would to take a picture.
Does the “ERR 99″ message appear? If so, then the CF card is the most
likely source of the issue. Try using a different card.
If the message does not appear, please complete the following steps:
1. Turn off the camera.
2. Clean the lens contacts by gently rubbing them with a pencil eraser
or soft cloth. Be careful that you do not let any debris fall into the
camera body.
3. Reattach your lens.
4. Turn on the camera.
5. Depress the shutter button as you would to take a picture." from [http://www.richardsnotes.org/archives/2005/04/29/50mm-lens-contact-points/|here.] Hope this helps, good luck.