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!

FS OBP XJVTYBOS YKE SKD MXI QPXE OBTR VS CQTPIE T XV TVGQPRRPE UPQS APJJ EKIP SKDQ RKJDOTKI NPS TR IQQXQYFFQKFB OBTR JTOOJP MBXJJPIYP AXR IKO OKK BXQE AXR TO