PA34 PLT HAD A RWY INCURSION AT PDK.

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ON STARTING SEP/XA/02 AT XA45; I WAS TAXIING FROM FBO AND GND CTL TOLD ME TO CALL THEM WHEN I MY RUN UP WAS COMPLETE FOR A RWY 2R DEP (IFR) IN VFR CONDITIONS. I CALLED GND CTL AND TOLD HER 'RUN UP COMPLETE.' I BELIEVE I WAS TOLD 'CROSS RWY 2L; HOLD SHORT RWY 2R FOR DEP; CONTACT TWR ON 120.9.' SO; I CLRED FINAL APCH COURSE FOR RWY 2L. THERE WERE NO ACFT APCHING AND TAXIED ACROSS TO HOLD SHORT RWY 2R. UPON REACHING THE HOLD SHORT LINE FOR RWY 2R; I CALLED TWR ON 120.9 AND SAID 'HOLDING SHORT OF RWY 2R FOR DEP.' TWR CAME BACK AND SAID 'YOU JUST CROSSED AN ACTIVE RWY WITHOUT PERMISSION.' I TOLD HIM I THOUGHT GND CTL HAD CLRED ME ACROSS RWY 2L. HE TOLD ME THAT THEY DIDN'T. THEN HE PROCEEDED TO CALL ME BACK AND TO CALL HIM UPON REACHING MY DEST. ON THE NEXT CALL I WAS CLRED FOR TKOF. I REPEATED BACK THE INSTRUCTIONS AND APOLOGIZED FOR THE MISUNDERSTANDING. UPON REACHING MY DEST; I CALLED HIM BACK ON THE NUMBER HE GAVE ME AND HE TOLD ME HE WAS GOING TO TURN THE RPT IN TO THE FSDO. HE SAYS GND CTL TOLD ME TO 'HOLD SHORT OF RWY 2L FOR RWY 2R; CONTACT TWR.' I GAVE HIM ALL MY INFO AND LEFT IT AT THAT.