As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER BRAKE RELEASE FOR TAXI, THE ACFT WOULD NOT MOVE. ENGINE POWER AND A PUSHBACK TUG HAD NO EFFECT. FOUND DURING OPERATION OF THE NR 1 HYD SYSTEM THAT THE LEFT BRAKES WOULD NOT RELEASE. PARKING BRAKE SYSTEM OK. REPLACED BRAKE CONTROL VALVE IAW AMM 32-42-06-00-801/400-801. RETURNED TO SERVICE.