Hello,
I have a Problem.

I won't play the Mulitplayer Modus. But when I logging in then come:
"An error has occurred. Please check your network connection "

What should I do?

I am from Germany.

I was having this on both the demo and now on retail. I found a youtube video that discusses it. On my Win7 I share my internet to other devices and so I have internet sharing turned on. you have to turn off internet sharing or bridge your LAN connection. It has at least allowed me to start to play in multiplayer for the FIRST time. before ALL i got was the error. here is a link to the youtube video. hope it helps in your case.
http://www.youtube.com/watch?v=Fikv2DpZNWU

Thanks, but I can't Sharing. Why this, I don't know.