What was found
DURING CLIMB, CETNER CARGO DOOR OPEN "A" ALERT MESSAGE. CREW FOLLOWED EMERGENCY PROCEEDURES AND RETURNED TO AIRFIELD. LANDING NORMAL. MAINT CHECKED CARGO DOOR IAW 52-32-04. MEL ASSIGNED FOR "A" SYSTEM, MEL 52-40-1-5, DMI 6803 ASSIGNED. AIRCRAFT RELEASED FOR SERVICE. FOLLOW UP: AT MIAMI, DMI 6803 MEL 52-40-1-5 CLEARED BY CLEANING DEBRIS FROM AROUND DOOR MICRO SWITCH. OP'S CHECK GOOD MEL CLEARED.