As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI, FWD EQUIPMENT VALAVE EICAS MESSAGE AFTER 2ND ENGINE START. VALVE LIGHT REMAINED ON AFTER COMPLETING QRH, A/C RETURNED TO GATE (BTB). MTX GROUNDED A/C. MTX C/W B767 FIM 21-58 FT 899. NO FAULTS FOUND SUSPECTED SHORT TERM POWER TRANSFER INTERRUPTION BETWEEN APU AND ENGINE SRAT. A/C REMAINS NON-ETOPS.AND RETURUNED A/C TO SERVICE.