ZID ARTCC RADAR CTLR ISSUES AN 11000 FT XING CLRNC TO A B737 THAT IS IN THE PATH OF A LJ35 AT 11000 FT.

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B737 WAS INBOUND TO IND; DSNDING TO 15000 FT. LJ35 WAS AN OVERFLT AT 11000 FT. I ISSUED TO B737 A XING CLRNC TO A FIX AT 11000 FT. I HAD ENTERED A TEMPORARY ALT ON THE B737'S DATA BLOCK OF 12000 FT; THINKING THAT IS WHAT I ISSUED; 12000 FT. TFC WAS ISSUED TO THE LJ35 THAT THE B737 WAS AT 1 O'CLOCK POS; 12 MI; NBOUND; AT 12000 FT. THE LJ35 DID NOT ACKNOWLEDGE THE TFC CALL. TFC WAS ISSUED TO THE B737 THAT THE LJ35 WAS AT 10 O'CLOCK POS; 12 MI; EBOUND; AT 11000 FT. THE B737 ACKNOWLEDGED THE TFC CALL. THE B737 DSNDED TO 11000 FT AND SEPARATION WAS LOST. I WAS SURPRISED THAT THE B737 DID NOT QUESTION HIS CLRNC TO 11000 FT AT THIS TIME SINCE IT WAS OBVIOUS THAT THERE WOULD NOT BE SEPARATION. SUPPLEMENTAL INFO FROM ACN 548053: I WAS 'CTLR IN CHARGE' AT THE TIME OF THE INCIDENT. I WAS BUSY PERFORMING SUPERVISORY DUTIES AND MANAGING THE AREA WHEN THE EVENT OCCURRED. I WAS NOT AWARE OF THE SIT UNTIL AFTER IT OCCURRED. CTLR DID NOT HAVE A D-SIDE AND WAS NOT BUSY ENOUGH TO WARRANT ONE. HE ISSUED TFC CALLS TO BOTH ACFT BUT NEITHER THE ACFT OR THE CTLR CAUGHT THE ERROR BEFORE THE CONFLICT ALERT ACTIVATED.