Here is a link for trouble shooting your problem. It will let you get a copy of the manual with phone numbers and everything. It means you will have to find the model number, but it helps. I have used it several times. The only thing I can think is that maybe the sensor has gone bad, but they can be a pain to trouble shoot without one of their specialists.

Here is a link that might be useful: find a manual for trouble shooting

Sounds like your lock button is stuck in.
If this is the Sears dark gray wall switch with a light gray lock button on the lower right corner,, it's not uncommon for it to stick in the depressed position.
If it looks like it's depressed, take the wall switch off the wall and fix it. It's only plastic, it will pop out easily.
You will need to gently pry the lighter colored top part off the switch (the part that has the glowing green light) and remove the screw. Then carefully slide the whole wall switch up about 3/8th of an inch and that will remove the wall switch.
Once you have re-set the lock switch, rather than depressing it again and having it lock on you, simply press the "learn button" on the back of the motor unit and then don't touch anything for 1 minute.
That should stop your wall switch from flashing.

Thank you so much GDS! It worked! No need to call repair man! Thank you thank you!