CPR X CLB THROUGH OCCUPIED ALT HAD LTSS FROM MIL Y. SYS ERROR.

Narrative

I WAS WORKING AT SECTOR 18 WITH A MODERATE TFC LOAD; THE 'D' SIDE WAS STAFFED. CPR X (ELGO) DEPARTED OQU AND AFTER RECEIVING THE ACFT FROM PVD APCH I CLBED THE ACFT TO FL390. SEVERAL ACFT WERE CHKING ON OR BEING CHANGED TO OTHER FREQS DURING THIS TIME. SECTOR 31 CTLR CALLED ME AND REQUESTED THAT I STOP X AT FL280 FOR TFC. I SAID I WOULD. THE OTHER CTLR THEN REQUESTED APPROVAL TO STOP MIL X (F-15) AT FL290 I APPROVED THIS AND HE DISCONNECTED. I THOUGHT THAT I THEN AMENDED X CLB TO FL280 AND CHANGED HIM TO SECTOR 31'S FREQ. ANOTHER ACFT CHKED ON DEPARTING BOS AND I CLBED HIM. A FEW MOMENTS LATER THE SECTOR 31 CTLR REQUESTED COMS WITH X. I TOLD HIM THAT I WOULD TRY HIM AGAIN. I ISSUED THE FREQ CHANGE AND RESPONDED. LISTENING TO THE TAPE OF THE INCIDENT; I DIDN'T HEAR MYSELF GIVE THE AMENDED ALT TO X. WHEN THE PLT CHKED ON SECTOR 31'S FREQ HE WAS STILL CLBING TO FL390. THE CTLR TOLD HIM TO MAINTAIN FL280 AND CALLED HIS TFC AT 2 MI AND AT FL290. THE F-15 SAID THAT X WAS WITHIN 300 FT BEFORE THEY WERE CLR. I FEEL THE PROB OCCURRED WHEN I LET MYSELF GET DISTR BY OTHER TFC IN MY AIRSPACE AND I DIDN'T ISSUE THE AMENDED ALT TO X.