ACR X CLB THROUGH OCCUPIED ALT HAD LTSS WITH ACR Y. SYS ERROR.

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WORKING LARGE SCALE; ONE HOLDING SECTOR 125 MI SCALE. STARTED MY SHIFT AT XX45. HAD AN ERROR AT XY42. PROB WORKING A LOT OF AIRSPACE. SCANNING WAS LIMITED. EXTRA PEOPLE AROUND COULD HAVE HELPED. THE CONFLICT ALERT STARTED WITH ACR X AND ACR Y. ACR X WAS CLBING TO FL220 AND ACR Y WAS SE AT FL190. I SAW ACR X OUT OF FL186 SO I EXPEDITED THE ACR X DOWN TO FL180 AND RPT REACHING. I PUT A J-RING ON ACR X. I CLBED ACR Y TO FL210 THINKING I COULD GET VERT SEPARATION. I THEN TURNED ACR Y 30 DEGS R AND THEN ISSUED TFC TO ACR X AND TURNED HIM 40 DEGS R. RIGHT AFTER THIS; I SAW ACR X MODE C READING FL206 AND THOUGHT THERE WAS NO WAY TO GET VERT BY DSNDING HIM. I WAS BACK TO ACR Y AND TOLD HIM TO MAINTAIN FL190 AND RPT REACHING. WHAT I SHOULD HAVE DONE DIFFERENTLY: ASK ACR X RATE OF CLB. TURN EACH ACFT L 40-50 DEGS. DSND ACR Y TO 15000 FT. VECTOR ACR X EARLIER FOR A SHORT CUT WOULD HAVE HAD LATERAL. SUPPLEMENTAL INFORMATION FROM ACN 257890: CTLR WAS CLBING ACR X TO FL220 THROUGH ACR Y AT FL190. WHEN IT APPEARED THERE WAS SEPARATION BTWN THE 2 ACFT; CTLR TRIED TO CHANGE PLAN AND REVERSE HIS PREVIOUS PLAN BY CLBING TURBOPROP AND DSNDING TURBOJET. WHEN THE CTLR INITIALLY RECOGNIZED THAT SEPARATION WAS NOT ENSURED; HE SHOULD HAVE STUCK WITH THE ORIGINAL PLAN AND SEPARATION WOULD NOT HAVE BEEN LOST SINCE ACR X WAS CLBING ABOUT 4000 FPM AND WOULD HAVE BEEN ABOVE THE TURBOPROP. THE OTHER OPTION WAS TO CLB ACR X TO FL180; WAIT UNTIL HE'D PASSED THE TURBOPROP; AND THEN CLBED TO REQUESTED ALT.