I have a canon 10D that is getting an "error 99".

Welcome to Fixya
Err 99 could mean several different things, such as... Memory Card, Lens or Lens contacts....

Here's what you can try:
Remove the memory card an enable "shooting with out memory card" and see if you still get the error. If it works your memory card is bad. Try another lens if you can. Clean the lens contacts with a pencil eraser (be careful not to get eraser dust in the camera body or in the lens). Worst case scenario is, Err 99 could be related to the shutter failing which would mean a trip to Canon.
Thank you

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Annoying - my 10D had the same issue. The camera maintains communication with the lens and if this is interrupted, you get the error.

You can try
a) cleaning the contacts - isopropyl alcohol on a Q-tip, do this for the lens and the camera. but be VERY careful not to drop alcohol anywhere.

b) remove/replace the lens

In my experience, neither of these solved the problem, but did decrease the probability of occurrence.

You can read here

Well, the EOS 10D is not a 35mm camera (that would be film, not digital) but there is software for it on the Canon website that you can download at THIS LINK

According to Canon, the battery should work in either camera. Does the battery work in the other camera but not in the 10D?

If the macro switch is held on the lens by 2 screws it is to old and will on work on your camera but if yous is a super type it may need a rechip

Yes, it is normal. This is a reasonably old DSLR, and it's designed for you to look through the viewfinder (it's more accurate anyway as it's looking through the lens). You'll find if you keep one hand under the lens and one hand on the shutter, it'll feel quite comfortable to look through the viewfinder.

You can still view photos you've taken after you've taken them though.

Was trying to use Sigma lens. Switched to Canon lens, problem solved.
Joe

Although you may have cleaned the lens contacts, did you clean the camera contacts? This is a bit harder but it’s doable: just hold camera so lens opening points down so no gunk falls in. Erase lightly. I used a lens cloth and dabbed at the contacts rather than blow them so as not to blow the erasings inside the camera.

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.
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 should be serviced.


From RICHARD'S NOTES

I get error 99 sometimes on my 20 D but it?s usually to do with a lens that is attached. Sigma lens have been known to cause error's. If it's not that or dirty contact on the lens then it could be a more serious problem. I would at least check it out with a canon dealer/repair centre.