As far as I know most drive's just check the region code mask at byte 35 in VIDEO_TS.IFO. Maybe your Xbox 360 (SD-S802A) "self-checks" if the drive has been changed to RPC1 ? Maybe it tries to verify RCE protection and if it can't then it will not let you play the disc ? I've heard the MS Vista OS does this maybe Server 2003 does too.

Isn't it easier to keep the drive RPC2 so you can change the drive's region code to match the disc instead of "the inverse" ?

bilm