As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT ABOUT 800 FEET AGL ON INITIAL CLIMB, CREW RECEIVED A RH REV UNLOCK CAUTION MESSAGE. THE CREW RAN THE QRH, DECLARED AN EMERGENCY AND RETURNED TO FIELD. THE CABIN WAS NOT BRACED, AND THE AIRCRAFT LANDED WITHOUT INCIDENT. MX REPLACED RH ENGINE THRUST REVERSER POWER DRIVE UNIT. OPS CHECK GOOD.