What was found
(CAN) UPON LOWERING FLAPS, FLIGHT CREW RECEIVED A "FLAPS FAIL" CAUTION MESSAGE. AN EMERGENCY WAS DECLARED AND THE ACFT LANDED WITHOUT FURTHER INCIDENT. ACFT WAS REMOVED FROM SERVICE AND MAINTENANCE FOUND THE LT WING OTBD SKEW DETECTOR GIVING 0.25 VOLT AT 0 OR 45. THE SKEW DETECTOR WAS REPLACED, TESTED AND THE ACFT RELEASED FOR SERVICE. AT THE TIME OF THE INCIDENT, THE ACFT WAS OPERATING WITH MEL 27-51-02-1. FOLLOW UP REVEALED THAT SKEW DETECTOR SN A1548 WAS INSTALLED DURING TROUBLESHOOTING OF THE "FLAPS HALFSPEED" STATUS MESSAGE THE NIGHT BEFORE.