Is the trolley (the thing the door and the chain is attached to) jammed against the bolt in front of the motor unit. If so, remove the bolt, turn the 'up limit' on the side of the unit about 3 turns in the opposite direction of the arrow printed on the cover. If it operates okay then replace the bolt.

Thanks for the suggestion but it didn't seem to help. I noticed that the l.e.d.'s on the safety sensors down by the floor of the door are not lit. I will try checking for voltage at the sensors. If ther is does this mean the sensors are misaligned or faulty. If no voltage then maybe a board issue?

If the small light is not lit on both of them check the wiring to the motor unit. If one is lit and the other is not make sure they are pointed directly at one another.