As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS NOT GROUNDED: SHORTLY AFTER SETTING FLEX POWER, INDICATION THAT THE #1 ENGINE THRUST REVERSER WAS UNLOCKED WITH REVERSE THRUST ENGINE NOISE. REJECTED TAKEOFF IMMEDIATELY BELOW 60 KNOTS. REPLACED BLOCKER DOOR STOW SWITCH IN LOWER RIGHT 4104KS2 POSITION WITH NEW IAW AMM 78-31-18, OPS CHECK GOOD.