What version of IE are you using???
Do you have a firewall up and running???
Something up with port 54???
This is what i got in reply to my questioning at invisionfree.com:
http://invisionfree.com/forums/support/ind...?showtopic=9044
Yeah - must be the firewall :(
and probably the same for me too, since this site works fine when I browse it from home.