Shoutbox

I have a serious problem with the voice chat. I have one copy of MSN Messenger at home with Plus! installed, all latest versions and it works perfectly. I have another copy at my office and I have never been able to establish a voice connection. I've tried almost everything there is to try, proxy, no proxy et al. Now I'm at a loss, I have no more ideas. Any one out there with a lightbulb over the head? Thanks for the help. Oh I forgot to mention: there is no error message, the connection is simply not established and after a minute or so the program gives up.