problem with net remoting

[BrightSoul]

hello, I have followed a tutorial on how to expose a class method over the net using net remoting.

All is working fine. I have 2 apps, one acting as a server:

TcpChannel channel = new TcpChannel(12345);
ChannelServices.RegisterChannel(channel);
RemotingConfiguration.RegisterWellKnownServiceType( 
         typeof(myclass), 
         "mymethod", 
         WellKnownObjectMode.Singleton );

and the other acting as a client:

TcpChannel chan = new TcpChannel();
ChannelServices.RegisterChannel(chan);
obj = (myclass) Activator.GetObject( 
         typeof(myclass),
         "tcp://localhost:12345/mymethod" );

I then tried to combine this two snippets into a single chat application. I wanted to run two instances of it and let them both act as client and server at the same time.
InstanceA calls mymethod on InstanceB
InstanceB calls mymethod on InstanceA
Unfortunately I get an error when I try to register the client channel after I registered the server channel. ie I get an error on the line in red:

TcpChannel channel = new TcpChannel(12345);
ChannelServices.RegisterChannel(channel);
RemotingConfiguration.RegisterWellKnownServiceType( 
         typeof(myclass), 
         "mymethod", 
         WellKnownObjectMode.Singleton );

TcpChannel chan = new TcpChannel();
ChannelServices.RegisterChannel(chan);
obj = (myclass) Activator.GetObject( 
         typeof(myclass),
         "tcp://localhost:12345/mymethod" );

what should I do? Is what I'm trying to do possibile in first place?
I cannot provide the exception description because the debugger just says "Application has generated an exception that could not be handled".
Many thanks in advance ^^