A FATIGUED AND TASK SATURATED EMB170 CREW WITH A HIGH MIN PNF CAPT OVERFLEW CLT 18R LOC AFTER A CLOSE-IN RWY CHANGE; FMS REPROGRAMMING; AND LOC NOT CAPTURING.

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FO; PF AND CAPT; PNF AND ON HIGH MINIMUMS. WE WERE ON REDUCED REST FROM THE NIGHT BEFORE AND WERE RUNNING LATE ALL DAY DUE TO NO APU; ACFT SWAP; AND NUMEROUS LOADING PROBS. APCHING CLT WE HAD TO BURN OFF FUEL FOR A FEW MINS TO MEET LNDG WT AND THEN GOT VECTORED TO RWY 18L. WHILE BEING VECTORED WE CHANGED THE NAV SOURCE FROM FMS (PINK NEEDLES) TO LOC (GREEN NEEDLES) ON BOTH SIDES. WE WERE ASSIGNED SPD 150 KTS AND 2 NM FROM FAF AND THEN CLT APCH ASKED US TO SLOW TO 130 KTS. WE TOLD APCH CTLR THAT OUR FINAL APCH SPD OF 138 KTS AND THEY ACKNOWLEDGED OUR SPD AND ASKED US TO CALL THE TWR. AFTER CHKING IN; CLT TWR ASKED US TO SLOW BECAUSE WE WERE OVERTAKING AN ACFT AHEAD. AGAIN THE CAPT STATED WE WERE AT 138 KTS AND THAT WAS OUR FINAL APCH SPD. AFTER JUST A FEW MOMENTS TWR CALLED FOR US TO GO AROUND AND ASSIGNED A DIFFERENT HDG AND ALT THAN THE PUBLISHED MISSED APCH. WE EXECUTED THE TURN W; BEGAN THE CLB AND CALLED CLT APCH WHO QUICKLY ASSIGNED A NEW RWY OF 18R AND TURNED US N FOR THE DOWNWIND. THE WORKLOAD INCREASED VERY RAPIDLY WITH NUMEROUS HDG AND ALT CHANGES WHILE RECONFIGURING THE AIRPLANE FOR THE NEW APCH. WE AGREED THAT THE CAPT (PNF) WOULD REPROGRAM THE FMS; SET UP RADIOS AND BRIEF THE NEW APCH. ALL CHKLISTS WERE COMPLETED AND THE AIRPLANE WAS PROPERLY CONFIGURED PRIOR TO OUR FINAL VECTOR TO JOIN RWY 18R LOC. AFTER RECEIVING THE APCH CLRNC TO RWY 18R; I SET THE INTERCEPT HDG AND SELECTED APCH MODE ON THE GUIDANCE PANEL. CLT APCH CTLR CALLED A FEW OTHER AIRPLANES AND THEN CALLED US TO SAY WE FLEW THROUGH RWY 18R LOC. I STILL HAD FULL DEFLECTION ON MY NEEDLE AND NO INDICATION WE FLEW THROUGH THE RWY 18R LOC. I TURNED THE AUTOPLT OFF AND IMMEDIATELY HAND FLEW THE AIRPLANE TO THE NEW HDG. AFTER VERIFYING THE NEW HDG AND ALT WAS PROPERLY SET WE RE-ENGAGED THE AUTOPLT. I THEN LOOKED AT MY PROGRESS PAGE TO VERIFY THE RWY 18R FREQ IDENT. THE PROPER FREQ IDENT WAS SET; HOWEVER ON MY SIDE THE FREQ WAS HIGHLIGHTED GREEN. I SELECTED FMS (PINK NEEDLES) AS MY SIDE SOURCE OF NAV; THE CAPT REENTERED THE RWY 18R FREQ AND I CHANGED THE NAV BACK TO LOC (GREEN NEEDLES). AGAIN AFTER VERIFYING EVERYTHING WAS PROPERLY SET; APCH MODE WAS SELECTED ON THE GUIDANCE PANEL AND THE AUTOPLT CAPTURED RWY 18R AND FLEW THE APCH WITHOUT FURTHER INCIDENT. MY FMS DID NOT ACCEPT THE CHANGE OF THE RWY 18R LOC EVEN WITH THE PROPER FREQ SET IN THE PROGRESS PAGE. I HAVE HAD THIS PROB BEFORE IN FMS NAV WITH PREVIEW MODE UP; BUT NEVER WHEN CHANGING FREQS WHILE REMAINING IN GREEN NEEDLES. WE LANDED WITHOUT ANY FURTHER PROBS AND ATC DID NOT REQUEST ANY FURTHER COM NOR ACTIONS CONCERNING THE INCIDENT.