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!

VS AOP RZQFXOAS XGJ SGE IRN HPRJ AOFB QS CHFPNJ F RQ FQLHPBBPJ KPHS MPZZ JGNP SGEH BGZEAFGN WPS FB JIJZZJQGHFOB AOFB ZFAAZP IORZZPNXP MRB NGA AGG ORHJ MRB FA