2001 Oldsmobile Alero Theft System

While driving my car one day the theft light on the dash came on with no drivability concerns. After shutting off the car and restarting it the light was off. A couple of days later I tried to start the car after comming out of the store all it would do is crank over and not start. Noticed the theft light on the dash flashing while cranking. I tried to relearn the PATS system by turning the key to the run position and letting it set for 10 min. Still no start. After trying this twice with no fix I tried another key with the same procedure and it started and quit right after. One more time and it started and ran fine for another day. A day or so after that same thing happened with the "good key". Once again the relearn seemed to work. Symptom is intermitent. A theft detected code was retrieved from the BCM. Any thaughts would be great. Thanks