AFTER A 1 MIN ARTS OUTAGE TO CHANGE SOFTWARE; AN IFR PA31 AT 6000 FT DID NOT TAG UP RESULTING IN THE ACFT ENTERING THE ADJACENT FACILITY WITHOUT COORD. HOWEVER; THE ADJACENT FACILITY CTLR WAS WATCHING THE TFC AND KNEW ABOUT THE TFC BEFORE ENTERING HIS AIRSPACE.

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MKG WAS CHANGING OVER TO ARTS IIE SOFTWARE. I WAS WORKING RADAR IN THE TWR CAB WHEN AIRWAYS FACILITIES CALLED TO TAKE THE ARTS OUT FOR 1 MIN TO REBOOT THE SYS. I WAS UNSURE WHAT THIS WOULD ENTAIL BUT AGREED TO ALLOWING THE ARTS TO BE TAKEN. I WAS WORKING A VFR PA28 PRACTICE ILS APCH TO RWY 32; VECTORING ANOTHER VFR PASE FOR LOC/BACK COURSE PRACTICE APCH TO RWY 14; MONITORING ANOTHER VFR IN THE N PRACTICE AREA; AND MONITORING ANOTHER VFR C172 INBOUND TO MKG FROM THE N FOR THE L BASE TO RWY 6. I HAD ACFT X; PA31; AN IFR OVERFLT AT 6000 FT LNDG IN ADJACENT AIRSPACE (8D4 SPARTA ARPT ACROSS THE BOUNDARY IN GRR APCH AIRSPACE). I WAS TOLD THE ARTS WOULD ONLY BE OUT FOR 60 SECONDS AND AT THE TIME I FELT THERE WOULD BE NO PROB. HOWEVER; IN TRYING TO SEQUENCE THE PASE REF THE PA28; I STARTED TO HAVE A CONFLICT WITH THE PASE AND THE C172. WHILE TRYING TO POINT OUT THESE ACFT TO EACH OTHER AND USING VFR ALT SEPARATION; THE ARTS CAME BACK ON LINE. HOWEVER; ACFT X DID NOT TAG OR DISPLAY A FULL DATA BLOCK TO ME ON MY SCOPE. ACFT'S DATA TAGGED WITH A 'C' CTL SYMBOL (NORMALLY USED TO REPRESENT A 'CTR' CTLR DATABLOCK) BUT NO DATABLOCK VISIBLE; THEREBY NOT MAKING ACFT X A VERY 'VISIBLE' TARGET TO ME. I ALLOWED MY ATTN TO BE DIVERTED TO MY VFR PRACTICE APCHS AND VFR INBOUND AND FORGOT ABOUT ACFT X. JUST AFTER ACFT X CROSSED THE BOUNDARY WITH GRR APCH; THE GRR CTLR CALLED RADAR ON ACFT X. I HAD NOT ACCOMPLISHED A PROPER HDOF NOR MADE ANY COORD WITH GRR UNTIL IT WAS TOO LATE. THANKFULLY; GRR WAS AWARE MKG WAS TESTING ARTS IIE AND THEY WERE CLOSELY MONITORING OUR BOUNDARY. IT WAS DECIDED THAT THE INCIDENT WOULD NOT BE CLASSIFIED AN OPDEV DUE TO THE GRR CTLR BEING AWARE OF ACFT X AND WAITING FOR ACFT X TO CROSS THE BOUNDARY AND THAT MKG WAS STILL TESTING THE ARTS IIE. NEXT TIME I NEED TO REMAIN MORE AWARE OF MY IFR TFC AND NOT APPROVE A TEMPORARY SHUTDOWN UNLESS I AM ABSOLUTELY SURE OF THE CONSEQUENCES. I SHOULD HAVE ALSO ASKED FOR ASSISTANCE FROM ANOTHER CTLR BEFORE LETTING AIRWAYS FACILITIES TAKE THE ARTS. ALSO; IT WOULD HAVE BEEN BETTER TO DELAY THE ARTS OUTAGE UNTIL ALL TFC WAS POSITIVELY SEPARATED. I WAS TRYING TO HELP WITH THE ARTS CHANGE-OVER WHEN I SHOULD HAVE BEEN MORE CONCERNED ABOUT MY FIRST PRIORITY -- PROVIDING A SAFE; ORDERLY FLOW OF AIR TFC. I KNOW BETTER THAN THIS BUT STILL ALLOWED MYSELF TO BE CAUGHT UP IN THE RUSH TO GET THE ARTS IIE GOING.