Is it always at the connection level or later it happens to disconnect you while you're already connected to the server ?
This error may be result of many things - happens to me too usually after some idle time, but this is other case than yours i suppose...
I can suggest that you may try to connect to other servers within the network, and/or use other ports (within range) than default 6667 for connection. You can do this by a command /server severname:portnumber - for example :
Also it may have something do do with your host/router communication if you have one... So in the end you can update firmware for your router or at least restart it if above notes won't help.
It's recommended to check your software firewall settings too, as the port range for IRC servers may be blocked in there...
That's all i could think about for now - maybe later someone will have any other ideas