I am glad I found this post, as I am having the same problem.
What is less encouraging is that there are no replies... *sigh*
It's super frustrating to be racing online in NFS Shift & suddenly get booted from the PSN ("and possibly EA Nation as well" as the game indicates.)
I asked the players I was racing if they were also kicked from the PSN and the game and they said they weren't. It was as though I just gave up and left the race!
Are we the only users of this router having this problem? I hope not. Any solution provided would appreciated

I have concerns as well about putting my PS3 into the DMZ.