This problem is defnetly Port based:
why ?
I myself had this problem ages ago but then i got my bnc (bnc on port 40000) now when this morning my bnc got disconected i saw the 10053 error after a few houres again.

When I try to connect to a diffrent server with default ports (6667-6669 , like quakenet where i'm at) he gives me the 10053 error , on the other hand when i connect to a server with port other then 6667-6669 like irc.insiderz.de (6661)
I get connected instantly (same with my bnc on port 40000)

Don't ask me howcome.

Internet: cable
Amd64 athlon 3000+
512 mb ram
SP2 win XP had it with SP1 to

I went to the www.quakenet.org site and looked for a quakenet server with a difrent server port then 6667-6669
AND got connected IMMEDIATLY !