As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED NLG GEAR OPEN DOOR OPEN LIGHT AND LGD CAUTION LIGHT DURING CLIMB. CREW DECLARED AN EMERGENCY AND RTF AND LANDED AT DEN WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE NLG DOOR CLOSED PROX SENSOR PER BOMBDR AMM, OPS CHECK GOOD.