This is an issue w/IPv6 for sure.
I had the same problem and stepped through the debugger. In the
AsyncSocket class, there are a few debug lines commented out. If you
uncomment it, you can see that if you try to connect from certain
machines, it resolves as IPv4 and in my case, connecting locally on
the server resolved the address as an IPv6 endpoint.
The solution for me was to set the JabberClient.Server property to the
IPv4 IP address.
For example:
JabberClient client = new JabberClient();
// Other init code here...
client.Server = "127.0.0.1";
The real solution probably involves making a change to the AsyncSocket
class or the Address class.