A CRJ200 FLAPS FAILED AT 20 DURING FLAP SELECTION FOR LNDG. A GAR WAS EXECUTED AND AN EMER DECLARED. AFTER THE QRH WAS CONSULTED A NORMAL LNDG FOLLOWED.

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WHILE ON VISUAL APCH WHEN SELECTING FLAPS 20 WE OBSERVED THE FLAPS FAIL CAS MESSAGE. THE FLAPS STOPPED AT 20 DEGS WITH NO ASYMMETRY. FO WAS PF. I NOTIFIED APCH AND ASKED FOR A VECTOR AND A CLIMB TO 5000 FT. I RAN THE QRH AND ONCE THAT WAS COMPLETE WE NOTIFIED APCH OF THE SITUATION AND DECLARED THE EMER. WE WERE VECTORED FOR A 10 MILE FINAL. I TOOK OVER PF DUTIES PRIOR TO TURNING INBOUND TOWARDS THE ARPT. WE FLEW THE APCH ON AUTOPILOT DOWN TO 500 FT. I THEN LANDED NORMALLY WITH FO CALLING OUT THE SINK RATE WHEN THE ACFT WAS BELOW 100 FT. THE TOUCHDOWN WAS AT LESS THAN 100 FPM SINK. NO SIGNIFICANT PROBLEMS WITH THE LNDG. THE ACFT WAS ON A FERRY FLT TO THE MAINT FACILITY FOR A FLAP PROBLEM. HOWEVER THE PROBLEM THAT THE ACFT HAD BEFORE WAS ONLY ON THE GND AND DURING RETRACTION. WHEN THERE IS A FLAP PROBLEM IT WOULD BE NICE TO ALLOW FOR MORE TROUBLESHOOTING AT THE ACFT'S LOCATION PRIOR TO CONDUCTING A FERRY FLT TO DELIVER IT TO THE MAINT FACILITY.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT ON THREE FLTS PREVIOUS TO THIS THE ACFT'S FLAPS WOULD NOT RETRACT FROM THE 45 DEG LNDG POSITION UNTIL THE FLAP CONTROL CIRCUIT BREAKER WAS RESET ON THE GND. AFTER THE THIRD EVENT; THE RPTR WAS ASSIGNED TO FERRY THE ACFT TO A MAINT BASE AND HAD THIS FAILURE OCCUR. WHEN THE ACFT ARRIVED AT THE HANGAR; MAINT LOOKED AT THE COMPUTER CODES AND FOUND A FLAP ASYMMETRY CODE INDICATED AS THE CAUSE OF THE FLAP FAULT. THE RPTR AND MAINT WALKED AROUND THE ACFT AND COULD NOT VISUALLY DETECT A DIFFERENCE BETWEEN THE FLAPS. CAN ONLY GUESS AS MAINT DID; THAT THE FAULT WAS CAUSED BY A PROXIMITY SENSOR. THE RPTR STATED THAT 'THERE HAVE BEEN A RASH OF THESE.'