OPERROR -- MISIDENTED ACFT.

Narrative

I WAS WORKING DEP E AND DECOMBINING THE POS (BRIEFING THE ARR CTLR); WHEN THE FIRST ACFT CALLED (ACFT A). I TOLD HIM HE WAS RADAR CONTACT AND TURNED HIM R TO 100 DEGS AND CLBED HIM TO 16000 FT. I NOTICED THE ACFT I IDENTED WAS SQUAWKING THE WRONG XPONDER CODE; SO I TOLD HIM TO SQUAWK THE RIGHT CODE; HE REPLIED 'I'M SHOWING THE RIGHT CODE; STANDBY 1 SECOND.' I THOUGHT HE WAS GOING TO FIX THIS PROB. WELL; A FEW SECONDS PASSED (ABOUT 15) AND THEN A SECOND ACFT CALLED (ACFT B). AT THIS MOMENT THE FIRST ACFT TAGGED UP AND WAS HEADED RIGHT FOR THE ACFT I HAD MISTAKENLY IDENTED. I IDENTED ACFT B AND TOLD ACFT B TO SQUAWK THE APPROPRIATE XPONDER CODE. I THEN IMMEDIATELY TURNED ACFT A FURTHER R HDG 120 DEGS AND EXPEDITED HIS CLB. ACFT A PASSED BEHIND ACFT B. ACFT A WAS 200 FT ABOVE AND CLBING AND 68 MI BEHIND ACFT B. THERE WERE 3 OR 4 FACTORS THAT CAUSED THIS TO HAPPEN. THE MAIN PROB WAS I MISIDENTED AN ACFT; BUT ADDITIONALLY; ACFT B WAS ON THE WRONG CODE; ACFT B WAS SUPPOSED TO CALL ME ON DEP FIRST BUT DIDN'T.