From the quakenet.org FAQ:
If you're trying to connect to QuakeNet and the server tells you that you have been K-lined or G-lined it means that you have been banned from QuakeNet, and the reason for that ban is *ALWAYS* sent out right after the server tells you that you are banned. Some scripts and bots (showdown, eggdrop) doesnt show this reason but just says that you're banned but there is always a reason given.

If you feel that you have been wrongfully banned or want the ban removed send an email to info@quakenet.org and include the reason for the ban, your host/ip, when it happened and anything else you think we need to know in order to remove your ban.