Quoting from the information page:
"6) If you operate a chat room using a third party server you may find its becoming unstable and dropping users as well as eating up enormous amounts of bandwidth, this is due to the large amount of malicious traffic crossing the primary network. The solution we ask you all to undertake is to unlist your chat rooms so that they do not appear on the WPN list, this will stop them being affected."
Whilst this works it is possible to overcome the problem by limiting the upload bandwidth for the server using other applications.
I am currently running 2 chatrooms, each with 2 doors, using the Ouka server. I also run the application 'Netlimiter' and use it to reduce the upload bandwith for each room to 3kB/s. By adopting this procedure the rooms I'm running appear on the WPN list with no difficulties.