Oh dear, I guess you have cracked the two caesar cryptos...
This one is more difficult. Although a simple substitution is easily cracked...
Again the characters are limited to A-Z... But I think I can come up with a 256 version again.

Enjoy!

RJ EMD KXVGUMEJ UNP JNS FKT LDKP EMGA VJ QLGDTP G KV GVZLDAADP IDLJ HDXX PNTD JNSL ANXSEGNT WDJ GA TLLKLURRLNRM EMGA XGEEXD FMKXXDTUD HKA TNE ENN MKLP HKA GE