Peter Rowe , Oct 17, 2010; 10:19 p.m.
Canon error code 01 is indeed an indication that the camera is having problems communicating with the lens. You might want to look at the contacts on the lens (and the camera) and clean them (Google it) - is there any black residue for example? If you had acess to another lens it would be a good test to see if it happens with that too. Right now though, the camera is telling you that the most likely cause is that the lens contacts are dirty. Also, make sure your battery is fully charged. You might also try the lens in manual AF and see if the problem still occurs.