ARTCC CTLR HAD LESS THAN STANDARD SEPARATION BETWEEN SMT CLIMBING AND MDT DESCENDING.

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SMT Y DEPARTED MDT ARPT ENRTE TO CVG REQUESTING FL350. MDT X WAS ENRTE TO IAD. SMT Y WAS ON A 270 DEG HDG CLBING TO 8000' AS PER HAR APCH CLRNC. MDT X WAS ON A 240 DEG HDG DSNDING TO 11000' AS PER MY CTL INSTRUCTIONS. THESE 2 ACFT WERE ON HDGS BECAUSE HAR VOR WAS OTS. I CLRED SMT Y DIRECT AIR AND CLB TO 16000' THINKING I WOULD KEEP 5 MI SEP WITH MDT X WHO WAS THEN CLRED TO 10000'. WHEN I SAW THAT LAT SEP WAS NOT ADEQUATE I THEN CLRED MDT X TO FLY HDG 270 DEGS AND SMT Y TO FLY 250 DEGS. THESE TURNS WERE NOT ADEQUATE TO ASSURE 5 MI AND SEEING THIS RATHER THAN GIVE EMER EVASIVE TURNS WHICH I BELIEVE WOULD CAUSE UNNECESSARY STRESS ON THE PLTS; I CLRED SMT Y TO CLB AT 10000' AND MDT X TO MAINTAIN 10500'; SINCE HE ALREADY DSNDED THROUGH 11000'. I SHOULD HAVE ASSIGNED HDGS THAT WOULD ENSURE LAT SEP BEFORE CLBING SMT Y THROUGH MDT X'S ALT. I BELIEVE A CONTRIBUTING FACTOR IS THAT HAR VOR NEEDS SERVICING FOR 1 MONTH. IT IS THE ONLY VOR IN SECTOR 27 AND IS NEEDED. IF MDT X WAS ON THE PREFERENTIAL ROUTING HE WOULD HAVE FLOWN OVER HAR VOR AND WOULD HAVE NEVER BEEN TFC FOR SMT Y. ANOTHER FACTOR THAT CONTRIBUTED WAS MY LACK OF EXPERIENCE AT THE SECTOR--APPROX 20 HRS. THE MAIN FACTOR IS THAT I ARRIVED FOR AN XB PM-XJ PM SHIFT AT XA45PM; THEN WORKED VARIOUS POSITIONS UNTIL XD05 PM WHEN I WAS RELIEVED TO TAKE A BREAK; BUT LEARNED THAT THE PERSON RELIEVING ME WAS SOMEONE ELSE'S RELIEF; SO I RETURNED 5 MINS LATER TO R27 AND HAD THE SYS ERROR AT XD44 PM. THIS MEANS THAT FOR 3 HRS OF WORKING MOSTLY BUSY TFC (I WAS COMING OUT OF HOLDING FOR PHL AT THE TIME THE ERROR OCCURRED) I HAD ONLY A 5 MIN BREAK. I BELIEVE THIS IS TOO LONG TO WORK BUSY TFC IN ONE STRETCH. I WORKED THIS LONG BECAUSE WE ARE SO UNDERSTAFFED AT ZNY. ALSO MY RELIEF WAS SUPPOSED TO BE A SUPVR WHO WAS CHATTING WITH ANOTHER SUPVR AT THE TIME OF THE ERROR.