I have 2 friends which had the "Lost Connection to Host" problem, they would get disconnected randomly within 2-10mins of joining a server. Both of them were using the same ISP but one of them changed and since changing to the new isp he hasn't had any lost connections whatsoever (my other friend which didn't change isp is still having the same problems)
My guess is the isp is blocking the ports or something along those lines...