What was found
(CAN) DURING INITIAL CLIMB FLIGHT CREW RECEIVED A LT REV UNLOCK CAUTION MSG. DECISION WAS TAKEN TO RETURN & LAND. THE ACFT LANDED WITHOUT FURTHER INCIDENT. IT WAS THE FOURTH SIMILAR PROBLEM REPORTED WITHIN A FEW DAYS. THE THRUST REVERSER WAS DEACTIVATED & THE ACFT RELEASED UNDER MEL. TROUBLESHOOTING LATER FOUND THE ENG THROTTLE GEARBOX LOCKOUT SOLENOID AT FAULT. THE GEARBOX WAS REPLACED, TESTED & A SUCCESSFUL TEST FLIGHT COMPLETED BEFORE RETURNING THE ACFT IN SERVICE.