DURING LNDG ROLL AT 100 KTS; CTLR ISSUED INSTRUCTIONS TO A B747-400 TO EXPEDITE TURNING OFF THE RWY DUE TO LNDG TFC ON SHORT FINAL. PLT MADE AN EFFORT TO CLR THE RWY AS INSTRUCTED AND IN DOING SO; CROSSED THE HOLD LINE FOR THE PARALLEL RWY CAUSING A GAR.

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THE ACFT WAS APPROX 645000 LBS ON TOUCHDOWN JUST SLIGHTLY BELOW MAX LNDG WT; OF 666000 LBS. DUE TO THE HVY WT THE APCH BRIEFING WAS TO CLR THE RWY AT THE LAST EXIT UNLESS WE WERE IN A GOOD POS AND SPD TO CLR AT AN EARLIER EXIT. AFTER BEING CLRED TO LAND AT APPROX 2000 FT THERE WERE NO FURTHER MESSAGES FROM THE TWR TO US TO INDICATE ANY SPECIAL REQUIREMENTS AFTER LNDG ACFT TOUCHED DOWN ON RWY 7R. DURING THE LNDG ROLL AT APPROX 100 KTS THE TWR ISSUED A SET OF INSTRUCTIONS WHICH WERE INTERPED AS 'TO CLR THE ACTIVE RWY AT INTXN E AND TO EXPEDITE THE EXIT AS ACFT WAS BEHIND US ON SHORT FINAL.' DUE TO THE URGENT YET UNTIMELY RECEIPT OF THESE ATC INSTRUCTIONS AS THE ACFT WAS STILL IN REVERSE THRUST AND AT 100 KTS VERY CLOSE TO EXIT E AND THE FO BEING THE HANDLING PLT AN IMMEDIATE XFER OF CTLS WAS MADE WITH NO TIME TO QUESTION OR ACKNOWLEDGE THE MESSAGE BY ME AS I WAS NOW THE HANDLING PLT CANCELING REVERSE; APPLYING BRAKES WATCHING OUT FOR THE EXIT AT E. I EXPEDITED CLRING THE ACTIVE RWY 7R AT EXIT E AS THE ATC HAD REQUESTED. AFTER CLRING THE ACTIVE RWY 7R I MOVED THE ACFT AS FAR AS POSSIBLE FORWARD ON EXIT E TO MAKE SURE MY ACFT'S TAIL WAS WELL CLR OF RWY 7R AS I ASSUMED THE ACFT BEHIND ME WAS A BIG JET AS ATC COULD NOT HAVE CLRED ANY OTHER ACFT TO BE LNDG SO CLOSE AFTER OUR ACFT A B747-400. ATC THEN ISSUED INSTRUCTION 'HOLD SHORT RWY 7L.' OUR ACFT HAD HALTED AND WAS WELL CLR OF RWY 7L BUT HAD TECHNICALLY BREACHED THE HOLD SHORT LINE OF RWY 7L. THEN TO MY SURPRISE THE ACFT BEHIND US (I BELIEVE A DASH 8 OR SMALL TWIN) FOR WHO I HAD PERFORMED THE EXPEDITING EXIT AT E FROM RWY 7R WAS CLRED TO LAND ON RWY 7L. SHORTLY AFTER ATC ASKED THE DASH 8 TO GO AROUND AT APPROX 150 FT AS TECHNICALLY RWY 7L WAS NOT CLR AS WE HAD BREACHED THE HOLD SHORT LINE. DASH 8 WAS ASKED TO DO A TIGHT CIRCUIT AND LANDED ON RWY 32 A FEW MINS LATER. TOO MANY INSTRUCTIONS FROM ATC AT A VERY CRITICAL PHASE IN THE LNDG ROLL.