As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT 0864 - DURING TAKEOFF ROLL AT LAS EN ROUTE FOR SFO WITH ENGINES AT 70 PERCENT THE TOGGLE SWITCH WAS PRESSED AND THE CONFIGURATION WARNING HORN SOUNDED. ABORTED TAKEOFF AND RETURNED TO GATE. MAINTENANCE PERFORMED A TAKEOFF WARNING SYSTEM TEST PER T/C A1B31009, TAKEOFF WARNING TEST CHECKED GOOD, COULD NOT DUPLICATE THE MALFUNCTION.