Auto-focus problems with EFS lenses

I have a 50d and three lenses. Both of my EFS lenses (50 1.8 and 17-85) will not auto-focus. When I attempt to auto-focus, it just constantly moves back and forth and never settles in. However, my 70-200 2.8 IS focuses perfectly.

Could this be something in the mounting areas of those types of lenses? Something a cleaning might help out with. Something else?

I don't use the EFS lesnes all that often and while I only have one body to test with now, I can't imagine it a problem with each lenses since they both have issues while my other non-EFS lenses does not.

Thanks for the guidance.

Matt