CTLR ISSUED TAXI INSTRUCTIONS TO ACR Y THINKING IT WAS ACR X THEN CLRED ACR X TO CROSS A RWY WHEN IT WAS ACR Y. SIMILAR ACFT TYPES.

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FIRST THING IN THE MORNING; AFTER I PLUGGED IN AND RECEIVED THE POS RELIEF BRIEFING; I FELT SLUGGISH -- 'BEHIND THE PWR CURVE.' I WAS INVOLVED WITH NWS FOR VISIBILITY CHANGES; CHANGING ATIS BROADCASTS; OBTAINING ENRTE SPACING PROGRAM TIMES; ISSUING IFR CLRNCS; COORDINATING WITH RADAR FLT DATA; AND TAXIING ACFT FOR DEP WITH UPDATED WX AND RVR. WE DON'T HAVE A LOT OF TFC AND THE MORNING 'MINI-RUSH' IS OVER WITH QUICKLY. I NOTICED THE TYPE ACFT ON THE ACR X FLT PLAN WAS AN LTT A BUT AN LTT B WAS PARKED THERE (WHERE ACR X IS USUALLY PARKED; AND I DIDN'T REALIZE IT WAS AN ACR Y LTT B). PARKED IN FRONT OF ME WAS AN ACR Z WAS ISSUED TAXI CLRNC; THEN I ISSUED ACR Y TAXI CLRNC TO THE ACTIVE RWY. (I WAS THINKING ACR Y WAS ACR X AND ACR X WAS ACR Z). AS THE ACR X WAS TAXIING; I WAS WORKING ON HIS ESP TIME AND WHILE WAITING FOR THE TFC MGMNT COORDINATOR TO ANSWER; I TOLD ACR X TO HOLD SHORT OF AN INTERSECTING RWY (ANTICIPATING HOLDING HIM ON THAT RWY IF HE WAS DELAYED TO LET OTHERS TAXI BY). I HELD HIM SHORT TWICE WITH NO RESPONSE; THEN; AS THE TFC MGMNT COORDINATOR ANSWERED; I HEARD AN ACFT ON THE SPEAKER BUT TALKED TO TFC MGMNT COORDINATOR AND GOT AN ESP TIME FOR ACR X. THERE WAS NO DELAY; SO I TOLD ACR X TO TAXI ACROSS THE RWY; WHICH HE WAS ALREADY DOING. THEN; ACR X (WHO WAS THE ONE ON THE SPEAKER WHILE I WAS ON THE LANDLINE) TOLD ME HE WAS PARKED AT THE RAMP. THIS WAS EXTREMELY EMBARRASSING AND MADE ME EVEN BUSIER BECAUSE NOW I HAD TO CANCEL ACR X AND GET ONE FOR ACR Y. I'M SURE I WOULD HAVE TAKEN SOME ACTION TO AVOID AN INCURSION; BUT THE PATH OF CONFUSION I LED MYSELF DOWN WAS SCARY.