a) restting my O2 Box2 to restore its system defaults but still has this issues.
b) logged in to the O2 Box2 as "SuperUser" and assigned the O2 ADSL's public IP Address (WAN address I believed) to this Xbox360's user through DMZ but it still gives me the same issues after rebooting. Noted that my nPnP is still enabled though.
Therefore UNLESS the O2 Wireless Box 2 is partly FAULTY, which I do not know as I don't have other equivalent Modem/router to test it. I'm on O2 Standard ADSL2+ (LLU instead of the ADSL Max). Do I need a NEW Modem/Router to replace the O2 Box2 in order to test this "restricted NAT" setting or I haven't done SOMETHINGS else in the O2 Box which may resolve this situations??
Thanks for any advices that I might have missed!!
P.S: My O2 Wireless Box2 is using 188.8.131.52 FW and is operating O.K in other aspects.
O2 Standard ADSL2+ Broadband!