I have a Canon EOS Digital Rebel XT with the original 18-55mm lense and a Quantarey 70-300mm lense. Have had all pieces for 3 years now and everything worked great until last night. Camera focuses and works fine with the small lense but with the zoom lense it will not focus and I get an Error 001 message????

This means that the communication with the Quantarey lens is not the right one.

You can try in cleaning the lens contacts and the camera contacts with a pencil eraser or a white erase (flip down the camera so no particles get inside the mirror box).

If still you are having problems, then that means the Quantarey lens is defective, and either needs to be service to be repaired, or you will need to get another zoom lens.

Best regards,