Take a dry can blower. Or if in lack, use an empty plastic bottle, without moisture inside, and use it to blow on the autofocus sensors.

They are located at the bottom under the mirror. NOTE Do not blow with your mouth, small amount of moisture will hit the CCD also located here.

Turn the camera off

Reattach the lens. Push the lens, white point to white point and turn the lens in place.

This worked for me, hope it also helped you ;)