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!

RW VKX NFAQMKVW MUB WUO CNT ZXNB VKQG AW DZQXTB Q NA QAJZXGGXB EXZW SXFF BUTX WUOZ GUFOVQUT PXW QG TZZNZMRRZURK VKQG FQVVFX CKNFFXTMX SNG TUV VUU KNZB SNG QV