Originally posted by bigted I however have no idea what that means and what one does when they clean the contacts.
"cleaning the contacts" just means to clean the brass looking electrical contacts on the lens and camera mount. If you take the lens off and look at the mount end you see a series of brass colored small metal balls poking through the mount. These are spring loaded electrical contacts that match similar contacts on the camera mount to allow communication between lens and camera. Take a soft micro-fiber cloth and buff the contacts a bit. Do the same to the camera contacts.
While you are cleaning take a careful look to see that all of the contacts are there and they are all in proper position, nothing sunk in.