I am having exactly the same problem with my 1/2 HP Craftsman garage door opener. I have deleted the codes and then reactivated the remotes three times. Within 5 minutes the door started opening and closing erratically non-stop until I unplugged the unit. After plugging back in and recoding, the same things happened. I ended up unplugging the unit overnight and recoding in the morning. So far so good. However, this has happened three times now over the last two years. Any ideas?

I have a craftsman 1/2 hp garage door opener and lost my remote control. I purchased a new one and tried to program it
using the learn button. The problem I have is when you push the learn button it is supposed to flash for a few seconds allowing it
to program the remote my light do not flash so I can't program the new remote. Has anyone has this problem? If so what was the fix? Thanks.