My garage door does not close in one push of the remote button or the wall switcxh. It moves down a short distance then stops and returns up. There is nothing in the way of the electronic eyes on either side of the door. The lenses are clean and the lights are green. The light on the unti does flash 4 times then a pause, thyen 4 times and so on. What's wrong? We have also replaced the batteries in the remotes to no avail.