(adsbygoogle = window.adsbygoogle || []).push({}); Why is the problem always apparently NAT type?
I have 3 PS3's in my house all connected to the same connection.
It just so happens that 1 of the PS3's cannot connect to a certain user yet we ALL have open NAT types.
Lets see you all tell me how to fix that!

Make sure your set the PS3's IP adresses on your Internet provider to open

maybe a silly idea, but worth a go.
try swapping the ps3's around, as in put the one that doesnt work into a room were a ps3 does work.
if that doesnt work, then you need to change the internet settings for that ps3 on your router.
please rep+ if i helped