Steven F , Oct 18, 2009; 07:05 p.m.
I don't have the 50D but to the best of my knowledge Canon doesn't have a error code for cleaning the contacts. In all likelyhood you are getting a Error XXX code for a problem with the lens or electrical contacts. The camera has no way of knowing if it is the contacts or the lens. Sometime the lens error can be caused by dirty contacts. However in many cases it is caused by a problem inside the lens.
Send the lens in for repair.