Normally this message means that either the server or the server host is down. One thing you can try is to ping the address through Windows, which will give results without going through mIRC.
To do this, if you don't know how, for Windows XP:
Start -> Run
Enter CMD <enter>
This will open a DOS window.
In that window type PING <address>
CMD and PING do not have to be in capitals and <address> is the address of the site you want to check.
In your case, it would be
