This lens works well on all bodies, the original rebel, 20D but doesn't work on the new Rebel T3i. No focusing, shutter won't work either. Don't know why. Thinking about returning the Rebel T3i I just bought from Amazon.
It should work on any EOS series body that accepts EF-S lenses, including Rebels. Do you have any other lenses to try out on the T3i? My guess is there's something going wrong with the body/lens electrical connection. Try removing/replacing the battery in the camera body, and removing/replacing the lens to make sure you have a nice firm connection.