ACR X DSCNT THROUGH OCCUPIED ALT HAD LTSS FROM MIL Y. SYS ERROR.

Narrative

ACR X WAS CLRED TO FL260. ACR X WAS STOPPED AT FL260 FOR MIL Y AT FL250 PROCEEDING DIRECT EWM. AT THE TIME OF THIS OCCURRENCE; I WAS ALLOWING A DEVELOPMENTAL (PLUGGED INTO THE D SIDE) TO ISSUE CLRNCS. ACR X RPTED ABOUT TO LEVEL AT FL260 AND REQUESTED LOWER. RELATIVE POS AT THIS TIME: MIL Y WAS IN THE ACR X 1 O'CLOCK AND 5 MI. AFTER ACR X REQUEST FOR LOWER; THE DEVELOPMENTAL ISSUED DSCNT TO 14000 FT AND GAVE THE TUS ALTIMETER. AT THIS POINT; I INTERVENED AND ISSUED A CLRNC FOR ACR X TO MAINTAIN FL260 AND CALLED TFC. THE RESPONSE WAS 'BLOCKED.' I AGAIN CLRED TO MAINTAIN FL260. THE ACFT RESPONDED 'CTR; WE'RE ALREADY OUT OF FL250 AND WE HAVE THE TFC; NO FACTOR.' AT THIS POINT CONFLICT ALERT ACTIVATED AND THE LOSS OF SEPARATION WAS RECORDED. SUPPLEMENTAL INFO FROM ACN 217148: ACR X WAS A TUS ARR OUT OF FL350 DSNDING TO FL260 BECAUSE OF MIL Y AT FL250. ACR X CALLED ABOUT TO LEVEL OFF. WITHOUT ANALYZING THE SITUATION; I CLRED ACR X DOWN TO 14000 FT AND ISSUED THE ALTIMETER. THE RADAR CTLR TRIED TO RECLR ACR X AFTER HE HAD ACKNOWLEDGED BUT HE WAS APPARENTLY 'STEPPED ON.' THE RADAR CTLR TRIED AGAIN BUT ACR X STATED HE HAD ALREADY PASSED FL260 AND THAT HE HAD THE TFC IN SIGHT. CONFLICT ALERT WAS ACTIVATED AND WE WERE RELIEVED OF THE POS. POOR JUDGEMENT; COMBINED WITH INEXPERIENCE ON MY PART; WERE THE PRIMARY CAUSAL FACTORS.