"insecure netblock" sounds like the server/servers have had probs with your ISP's customers, like virus or misbehaving, so it may not be aimed at you specifically.
In addition, part of the problem may be that "no ident response" line, it may be they require you to enable ident. Please see
this thread on enabling identd Most networks have a ton of info on their websites that addresses questions like yours, and Undernet is no excpetion. Read
http://www.user-com.undernet.org/documents/k-gline.txt for help and who to contact about the kline. Klines can only be resolved by the admins of the network involved.
Btw, posting on
Undernet's Forum will get you more Undernet specific help.