I have a problem with the camera recognizing the 20x lens.
The camera gives the check lens warning even though the lens is correctly installed.
When a second 20x lens is attached to the same camera everything is fine.

What would cause a lens not to be recognized by the XL2?

Thank you,
Bill

If you have access to another XL body, see if you get the same warning with that lens. If so, then the lens most likely needs to go to Canon factory service for a thorough inspection.

Try checking the 20 X lens contacts to see if they are unclean or slightly damaged/marked, and also check that the bayonet connection is clicking firmly into the correct position.

I had that problem with my 3xxl lens. About three minutes after the mesage went on, the image went to black.
Sent it into Canon for fixing, and got it back a week later working wonderfully.