My canon 20d stopped taking photos for no aparant reason. Kept getting error 99 and when I re insert the battery it starts clicking on it's own whether turned on or not. I sent it to Canon repair who wanted to charge me more than it was worth to repair but that was before they even started to analyse the problem. I decided to buy a brand new 20d. Put in the battery and the CF card and exactly the same thing has happened. I can get the cameras to come on but when I press the buton the flash jumps up and it says busy. I cannot get anything on the screen on either camera live view or menu etc. I have bought a new CF card in case it was that but all still the same. So I have 2 cameras doing exactly the same and I just don't know what to do HELP

If two cameras are doing it, I would suggest the contacts on your lens are dirty.

Try the following diagnosis steps for solving ERR 99 issues : -

To isolate the cause of the issue, 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 only 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 so, the camera may be faulty and requires a service. If it does not, then: -
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 faulty. Try a different card. If the message does not appear: -
1. Turn off the camera.
2. Clean the gold contacts on the lens by GENTLY rubbing them with a pencil eraser or soft cloth. Keeping the camera face pointing down, also clean the gold contacts on the camera, being 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.

If the “ERR 99" message only appears when one particular lens is attached, then that lens should be examined by a service technician.
If you see the “ERR 99" with a different Canon lens attached, then the camera is faulty and should be serviced.