Forums Connection Issues Invalid argument

No one really seems to know what to do with this one. My friend's internet is working perfectly, except for mIRC. The problem has to be in the computer itself, because they changed ISDN to ADSL and the error message didn't change.

So, everytime I try to connect to whatever existing server (I've tried many different servers and networks), it says "Invalid argument". I searched these forums and google, and everything I found out was some advice like "turn off your firewall"... It was turned off before I did anything. I've tried un- and reinstalling mIRC with default options, nothing changed. The funny thing is, it worked before, and suddenly it just didn't. Before this error message the message was, if I remember correct, "Socket not connected". It also changed suddenly.

So, is my friend doomed or has somebody got some ideas what to do?

edit: The platform is Win XP and I've used the newest available versions of mIRC all the time.