DIAGNOSIS The up travel limit is set too far. The door is traveling past its mechanical stop, triggering a safety reversal that interprets the event as an obstruction.
FIX Adjust the up limit switch. Locate the adjustment screws on the motor unit. Run the door to the fully open position. Turn the 'Up' limit screw clockwise in small increments (1/8 turn). Run the door. Repeat until the door stops just before it would strain against the opener's mechanism.
IF THAT DIDN'T WORK The safety reversal may be due to a weak signal from a remote. The door may be receiving a second 'close' command from a faulty remote button that is sticking. Remove the batteries from all remotes and test operation using only the wall control panel.
HEADS UP Improperly set travel limits are the primary cause of erratic door behavior. After adjusting the up limit, re-check the down limit to ensure the door still seals properly on the floor.