As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT CREW PERFORMED A LOW SPEED ABORTED TAKE OFF (50 KNOTS) AFTER RECEIVING A MASTER WARNING AFTER FLEX SET INDICATING CONFIG WARNING PARK BRAKE SET. THE PARK BRAKE HASN'T BEEN SET SINCE LEAVING THE GATE. THE AIRCRAFT RETURNED TO THE GATE WITH NO FURTHER INCIDENT. AIRCRAFT WAS GROUNDED. MAINTENANCE PERFORMED AN OPERATIONAL TEST OF PARKING BRAKE SYSTEM PER AMM 32-45-00-710-001-A, NO FAILURES DURING TEST. ALSO PERFORMED BSCU GROUND SCAN PERAMM 32-42-00 AND NO FAULTS NOTED.