SMA OFF ALT DUE TO ALTIMETER MALFUNCTION. ACFT EQUIP PROB.

Narrative

I WAS LEVEL AT 6600 FT WHEN ATC INFORMED ME OF A KING AIR DSNDING TO 7000 FT AT MY 11 O'CLOCK POS. I TOLD ATC THAT I WAS LOOKING; NEGATIVE CONTACT. I HEARD ATC NOTIFYING THE KING AIR. THE KING AIR CAME ON STATING THAT HE HAD THE TFC IN SIGHT APPROX 10-15 SECONDS LATER. AT THE TIME OF HIS XMISSION I SPOTTED THE KING AIR AND IMMEDIATELY UPON HIS ACKNOWLEDGEMENT BY ATC; RPTED THAT I TOO HAD HIM IN SIGHT. ATC THEN SAID TO ME; 'I SHOW YOU AT 6900 FT; WHAT IS YOUR ALT?' I STATED 6600 FT (ALTIMETER SET PER ATIS 29.99). ATC THEN SAID I CALLED YOU 3 TIMES; YOU NEED TO PAY ATTN. IT IS MY BELIEF THAT THEY DID NOT CALL 3 TIMES AS I CALLED TO NOTIFY THEM IMMEDIATELY UPON THE ACKNOWLEDGEMENT OF THE KING AIR'S SIGHTING OF ME. THE TOTAL TIME FROM FIRST XMISSION UNTIL THE CALL FROM ATC THAT THEY HAD CALLED ME 3 TIMES WAS APPROX 30-40 SECONDS. THERE WAS NO NEED FOR EVASIVE ACTION ON MY OR THE KING AIR'S PART. I THEN ASKED TO LEAVE THE FREQ TO OPEN MY VFR FLT PLAN UPON WHICH I WAS TOLD TO SQUAWK 1200 AND FREQ CHANGE APPROVED. I RESPONDED BY ASKING WHICH APCH CTLR TO CALL TO CONTINUE FLT FOLLOWING. CMH ATC THEN SAID STAY WITH ME FOR 10 MINS. I COMPLIED. AFTER APPROX 2 MINS ATC SAID NOTIFY MANSFIELD ATC UPON RETURN FROM OPENING YOUR FLT PLAN. I DID SO ONLY TO FIND THAT NO HDOF HAD BEEN MADE AND MANSFIELD; SAID I SHOULD BE IN CONTACT WITH COLUMBUS ATC. WHEN I EXPLAINED THAT COLUMBUS HAD TOLD ME TO CONTACT MANSFIELD THEY ASSIGNED ME ANOTHER SQUAWK CODE. LATER I VERIFIED MY ALT WITH TOLEDO APCH. AFTER CONFIRMING ALTIMETER SETTING AND WHILE STABLE AT ASSIGNED ALT; THEY STATED THAT THEIR RADAR INDICATED ME TO BE 200 FT ABOVE MY ALTIMETER READING. UPON ARR AT MY DEST I INFORMED THE FBO OWNER OF THE DISCREPANCY (RENTED ACFT) AND HE SAID HE WOULD CHK TO CONFIRM ACCURACY.