As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIVERTED TO DEN DUE TO THE CAPTAIN AND FIRST OFFICER'S VMO-MACH WARNING INDICATOR BOTH STUCK AT 265 KNOTS. *S/D* THE VMO-MACH ALT GUARD SWITCH WAS FOUND SAFETIED IN THE ALT POSITION. REPOSITIONED SWITCH TO NORMAL, OPERATIONS CHECK NORMAL.