B757 ACFT ON STAR ARR HEARD; RESPONDED; AND SET 11000 FT AS ASSIGNED ALT. ARTCC RADAR CTLR TOLD THEM THAT THE ASSIGNED WAS 12000 FT SO FLC CLBED TO 12000 FT.

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DSNDING INTO MCO; N OF OMN ON BITHO 7 ARR; HAD PREPROGRAMMED FMC TO EXPECT LAMMA 250 KTS; 12000 FT. FO FLYING. I WAS BUSY MONITORING RTE AND RADAR DUE TO TSTM IN AREA; TALKING TO PAX; AND ADVISING FLT ATTENDANTS. CLRED TO CROSS LAMMA AT 250 KTS AND (I SET 11000 FT IN MCP)? FO POINTED TO AND ACKNOWLEDGED ALTIMETER SET PER SOP. LEVEL AT 11000 FT AND APCHING LAMMA; CTR TOLD US TO CLB TO 12000 FT. I ACKNOWLEDGED BUT SAID WE WERE AT 11000 FT ALREADY AND DID HE ACTUALLY MEAN CLB TO 12000 FT. CTLR SAID OUR CLRED ALT HAD BEEN 12000 FT; NOT 11000 FT. WE ACKNOWLEDGED BUT TOLD CTLR WE UNDERSTOOD WE HAD BEEN CLRED PREVIOUSLY TO 11000 FT. SUBSEQUENTLY CLBED TO 12000 FT AND WERE CHANGED TO ORL APCH. WITHOUT LISTENING TO ATC TAPES; I HONESTLY DON'T KNOW WHETHER CTLR ERRED (MISSPOKE) OR WHETHER WE WERE AT FAULT. ALL OUR SOP'S ARE DESIGNED TO PRECLUDE SUCH AN OCCURRENCE (TO PREVENT OUR FAILURE) AND WE FOLLOW THEM RELIGIOUSLY. BOTTOM LINE: A MISTAKE WAS MADE EITHER BY ATC OR BY US; AND THE PROCS USED BY ALL SHOULD HAVE; BUT DID NOT; PREVENT THE ERROR. I DO NOT THINK CHANGES TO SOP OR PROCS ARE WARRANTED. THE GOOD NEWS IS THE SYS IS WORKING! THE ERROR WAS CAUGHT AND CORRECTED IN A TIMELY MANNER -- REGARDLESS OF THE ERROR SOURCE!