A few suggestions:

- I have seen in the past people have issues with mIRC auto-opening URLs. Perhaps there is a website link in one of the MOTD files of a server on their network? Try disabling the URLs Catcher in mIRC if it's enabled: ALT+O > IRC > Catcher (Uncheck 'URLs' under 'Enable catcher for:') Also try typing /!remote off before connecting.

- The vast majority of networks scan all connections with an open proxy monitor, some of them work in different ways. Note this message when connecting:

-ServerName.ChatNet.Org- *** Notice -- This server runs an open proxy monitor to prevent abuse.
-Servername.ChatNet.Org- *** Notice -- If you see connections on various ports when you connect
-Servername.ChatNet.Org- *** Notice -- please disregard them, as they are the monitor in action.

It could be that your firewall is sensitive towards this? I don't know what the relation to sex sites is, but I don't know how their proxy monitor works....they seem to use BOPM (Blitzed Open Proxy Monitor). Some more info can be found on this page of their website.

- You may want to contact a Server Administrator or other form of Administrator on Chatnet and see if this is a known issue. Search their website.

Like Krejt I have no issues connecting to Chatnet.

Regards,