I have a canon eos 20d that has become permanently attached to a canon 75-300 zoom lens. I cannot detach the lens and fear if I force it it will break the camera and/or lens. The lens is more than 5 years old, and camera 2 years old.

a 550D is a detachable lens camera and will not auto-zoom (it has a rubber ring that you turn to accomplish this with most lenses). are you sure you have an EOS 550D, or did you mean auto-focus?

It's a frustrating catch all error and needs service.The camera may have any one of numerous issues or lens issues. If you have more than one lens, see if the error occurs with both lenses on. If not then it's a lens error. A camera repair facility can plug unit the camera and download a more accurate troubleshooting code. Royal Camera Service in Hanover Park, IL is good source for this problem. The replaced the shutter on my 20D when I got the error 99 code.

1.Remove the battery, lens and CF card. Allow the camera to sit without power for 20 minutes and then reinsert a fully charged battery.
2.Turn the camera on and push the shutter button as if you were taking a picture.
3. If you don't get the error message reattach the lens and insert the CF card.
4. Check the below canon eos 20d service manual link:
http://goo.gl/YtVLQR

it will help you to save a lot of money
Hope it helps, Thanks

I had the same problem with the same lens. Over a few months it got lose, eventually getting so sloppy that it dropped if my 40D was held down. 10 days ago it jammed and the zoom was locked. I sent it to Canon and received it back in a week and it is now like new. Please don't try and fix it leave it to the experts at Canon. Not sure what the cost was as mine was still just under warranty
I think that this is a common problem with this lens and beleive that something in the lense works loose and eventually drops into the mechanism.

Some of the long tele's like that have some sort of locking mechanism on the side to prevent lens creep. Look for switches other than your aperature lock and auto focus/manual switch.

There is a lock on some of the OEM Cannon lenses underneath the lens. I didn't know it was there until having it for a year. Check to see if you have one and also remove and reattach the lens several times. You can try going to Ritz camera or Calumet to see if they can help you. Ask them who their Canon expert is. blessings!

Error 99 is a NONSPECIFIC error message. It is almost always associated with the LENS. I first got this error on my EOS 20D whei I tried to use an older Sigma zoom lens (7 years older than the camera). I don't use off-brand lenses with my Canons. Try removing the main battery first followed by the time & date battery which is hidden in the battery compartment beside the main battery. This will reset your camera. Good Luck!

Hi there,
The autofocus mechanism on some lenses can be damaged if you manually focus while the camera is attempting to autofocus. Basically, you would be working against the motor and gears. 
There is no need to download software before using the camera, however, I would suggest going to Canon's website and downloading the firmware upgrades for it. Here's the link:
Canon 20D Firmware Download
Hope this helps!

HI BRIAN ,,I AM SAGHA CAMERA REPAIRER,I THINK UR PROBLEM OCCURS DUE TO JAMMING OF PLASTIC MOUNT ON THE METAL BODY OF 20D.TRY THIS

1} LUBRICATE THE JUNCTION WHERE LENS GET ATTACHED TO THE BODY WITH KEROSENE THEN TRY TO RELEASE THE LENS.REMOVE THE BATTERY FROM CAMERA ,TRY AND HEAT UP THE JUNCTION WITH HAIR DRYER A LITTLEBIT THEN TRY TO RELEASE THE LENS.

2}IF THIS THING ALSO DOESN'T WORK THEN YOU HAVE TO SACRIFICE THE LENS PLASTIC MOUNT PUT SOME SHARP KNIFE LIKE OBJECT IN THE JUNCTION OF LENS & CAMERA & THEN PUSH IT UPWARDS WHICH WILL BREAK ONE OF THE PLASTIC LENS MOUNT COLLOR AND LENS WILL COME OUT WITHOUT DAMAGING YOUR CAMERA .LATER YOU CAN GET REPLACED THE LENS MOUNT FROM SERVICE PERSON. BUT NOW ATLEAST YOU CAN USE CAMERA WITH OTHER LENSES.

There is a website devoted to Err99: http://www.richardsnotes.org/archives/2005/04/29/50mm-lens-contact-points/

I have a Quantaray 100-300 which also displays an Err99 when used in automatic mode. The only way I can use this lens is in AV mode and select the widest aperture.