AN ACR MLG CREW MISINTERPRETED A PLT'S DISCRETION CLRNC AND DEVIATED FROM ITS ASSIGNED ALT.

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AFTER BEING CLRED DIRECT BUF AT FL290 WE WERE GIVEN CLRNC TO CROSS BUF AT 11000 FT; PLT'S DISCRETION; BY ZOB. SHORTLY AFTER; WE WERE TOLD TO DSND TO FL280 FOR TFC. AGAIN; AFTER LEVEL OFF DSND TO FL270. THE FO WAS NOW OFF ATC TO COPY THE ROC ATIS. ABOUT THIS TIME; CLEVELAND SAID WE WERE CLRED TO FL240. AGAIN; DSCNT WAS STARTED AND A LEVEL OFF AT FL240 WAS MADE. APPROX 42 DME SW OF BUF I STARTED A DSCNT TO CROSS BUF AT 11000 FT. A CALL TO CTR ON LEAVING FL240 WAS NOT MADE DUE TO FREQ CONGESTION. AS WE WERE APCHING FL230; CTR ASKED IF WE WERE MAINTAINING FL240. WE REPLIED WE WERE DSNDING TO CROSS BUF AT 11000 FT. CTR SAID OUR CLRED ALT WAS FL240 AND WE WERE NOW CLRED TO MAINTAIN FL230. OF COURSE; TO US; CTR WAS NOT CLR IN TELLING US PLT'S DISCRETION TO CROSS BUF AT 11000 FT WAS CANCELLED. WE INCORRECTLY ASSUMED THE BUF XING WAS STILL VALID AND INTERIM DSCNTS TO FL280; FL270; AND FL240 WERE TO GET US BELOW OTHER TFC. IT WAS NOT EVIDENT TO US FL240 WAS A HARD ALT. PERHAPS A COMMENT BY CTR THAT 'PLT'S DISCRETION' TO CROSS BUF WAS CANCELLED AND MAINTAIN FL240 WOULD HAVE NOT CAUSED THE CONFUSION. ALSO WERE WE ABLE TO PROMPTLY RPT LEAVING FL240 THAT WOULD HAVE AVERTED THE MISUNDERSTANDING.