Commerce gateway problems

I am trying to connect biztalk with navision but i am getting errors. In event viewer there are messages like When i run Biztalk 2004 system check.

Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host

and also the error :

Object reference not set to an instance of an object.

What must be the problem? Do i have to install the broker?

I have installed the broker and it is working somehow now. I have noticed and also before the Navision manuals are not really clear. You have to do a lot of tries before the systems really works.