PlusNet SpeedTouch 585v8 - Xbox Strict NAT

[#1]

I am getting a strict NAT on my 360. It doesn't happen with any other router.
Any ideas?

[#2]

Xbox live is one of the preconfigured applications in the setup pages on the router, so all you should need to do is select that and point it at the xbox's IP (may well be worth giving the xbox a static IP before doing this if you haven't already).