You don't have the server in your cache, there's an issue with their DNS right now
I don't know much more about the issue, but I do know how to fix it:
[15:30] <&Peter> 94.75.198.6 for maple
[15:30] <&Peter> 85.17.97.63 for triton
[15:30] <&Peter> 81.171.82.30 for ds9
basically instead of /server irc.gtanet.com use /server 94.75.198.6