The 20D is tossing this error

The 20D is tossing this error. If I test the camera with no lens I get no error. That suggests the interface between the camera body and lens.

• Using the factory lens EFS 17-85 F4 (“X”) and the contacts cleaned sometimes it works, most times I get the error 99.
• Using the Sigma telephoto 70--210 F4 (“Y”) and the contacts cleaned sometimes it works, most times I get the error 99
• Using my lens 5D’s lens US 24-105 F4 (“Z’) It works, each and every time. Literally hundreds of photos

This suggests to me that the problem is the connection with the lenses X and Y. That is not fixed by cleaning the contacts. Might be the contacts are worn (or???)

So before I go and buy another lens, I want some other opinions