As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
EICAS MSG ALT DISAGREE(CAUTION) IS DISPLAYED IN CRUISE FLT NOTE CA - 3100 STBY 31180 FO 30800. CREW ELECTED TO RETURN TO MIA. MAINTENANCE GROUNDED AIRCRAFT. MAINTENANCE PERFORMED FIM 34-12 FAULT TREE 804, PERFORMED CAPT/FO HIGHT RANGE LEAKAGE TEST IAW 34-11-00/501 LEAKS IN LIMITS. ALSO REPLACED RT AIR DATA COMPLUTER IAW AMM 34-12-01/401 INSTALLATION TEST NORMAL. AIRCRAFT REMAINS RVSM OPERATIONAL PART EFEECTIVITY VERIFIED. AIRCRAFT RETURNED TO SERVICE.