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!

BY VGO JCSWUGVY UFP YFH IJN KOJP VGWR SY AKWONP W JS WSEKORROP DOKY XOCC PFNO YFHK RFCHVWFN MOY WR OAIGIOUWGOUN VGWR CWVVCO IGJCCONUO XJR NFV VFF GJKP XJR WV