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!

QE OBZ MSJKPBOE PFH EFX WMT AZMH OBKY JE IAKZTH K MJ KJVAZYYZH RZAE DZSS HFTZ EFXA YFSXOKFT CZE KY TAAMAPQQAFQB OBKY SKOOSZ WBMSSZTPZ DMY TFO OFF BMAH DMY KO