I finally got a new lens for my camera, got myself a SIGMA 70-210MM F/4-5.6 UC LENS FOR CANON EF MOUNT. The price was pretty good which is why I got it. But now I'm having trouble. I was told this lens would work with my camera, a Canon EOS Rebel XTi, but when I try to take a photo it tells me Err99 Shooting is not possible. Turn the power switch of to <off> and <on> again or re-install the battery. Did I get the wrong lens? What can I do to fix this problem?