As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE CREW REPORTED THAT AT FL 320 WITH AUTOPILOT ENGAGED, WE RECEIVED EICAS "AP ELEV MISTRIM". THE CREW DISCONNECTED THE AUTOPILOT AND SHORTLY AFTER RECEIVED EICAS "PTRIM MAIN INOP". THE CREW DECLARED AN EMERGENCY AND UTILIZED BACKUP PITCH TRIM FOR LANDING. THE ACFT WAS REMOVED FROM SERVICE. R & R THE HORIZONTAL STAB ACTUATOR IAW AMM 27-40-02. THE OPS CHECK WAS GOOD. THE ACFT WAS RETURNED TO SERVICE.