11-19-2012 11:39 PM
I'm sorry to hear of the trouble you've encountered with focusing on your EOS 600D.
First, please ensure that the "AF/ MF" switch is fully in the "AF" position.
Next, I recommend cleaning the lens contacts using a clean piece of Micro fiber cloth. Please clean the contacts on the lens and the camera. Only light pressure is required. Please take precautions to prevent any debris from entering the camera.
If the issue persists, does this happen with all your Canon lenses? If not, which lenses are affected?