I was able to fix this problem this morning.

Firstly, I opened all the ports required for the Playstation Network as described in the guide for my router at portforward.com
http://www.portforward.com/english/routers/port_forwarding/routerindex.htm

Then it still failed.

But when I went on the PS3 XMB screen and went to Network Settings and turned OFF Connection to Media Servers...

POOF! It worked right away.

dutchman

I cannot thank you enough! I've been looking for this solution for months on the web. (me I was having the problem with GTA 4, couldn't play online). Well thanx for the post man, really appreciated!