I bought a kit with a Canon EF 75-300 f/4-5.6 lens with a Vivitar Series 1 2XMC4 AF teleconverter. I have a Canon 6D. The camera reads F00 when hooked up and says there is no lens attached.

SOURCE: Why do I get Error 99 in my Canon EOS 350 D?

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.

SOURCE: Canon Rebel T1i

I have the canon 70 -300 sitting right here beside me on my XTi, it also fits my XSi and all my EOS mount film bodies. one thing about canon EOS lenses and bodies: They fit and work together. Yes there are cheaper lenses, but I just answered another question on this website from somebody who has a 3rd party lens (and a high quality lens ta-boot) that will not work on his canon. This is typical of canon. They do not release all of their codes to 3rd party manufactures. Your friend just bought a premium camera, do not let him put a lesser lens on the camera, he will not be happy and the savings will not be that significant to make up the difference...

SOURCE: Would this lens work with my digital canon

HI
IF the lens has a macro switch that is fixed to the
lens by two screws it is a old type lens and will not
work on digitel and it can not be upgraded