I am on the case. One of the network's very own IRCcops is currently looking into this as we speak.
Edit: Here's a transcript of the conversation I had with the IRCcop concerning this issue:
[13:28:39] <FireSeraphim> Fudge, it seems that some peeps wishing to join #cvdungeon are having issues. I believe they may have fallen victim to some old ranged ban
[13:29:01] <FireSeraphim> allow me to link you to a forum topic where the grievance has been reported
[13:29:01] Fudge [Fudge@staff/Fudge] has just joined #cvdungeon
[13:29:01] Common channels for Fudge [Fudge@staff/Fudge]: #smbx, #cvdungeon, +#help
[13:29:23] <FireSeraphim>
http://castlevaniadungeon.net/forums/index.php/topic,5727.msg124897.html#new[13:31:54] <FireSeraphim> Fudge?
[13:31:55] <Fudge> You could clear the bans on that channel; /cs clear #cvdungeon bans
[13:32:04] <Fudge> I believe that would work, though I've never needed to use it
[13:32:29] <FireSeraphim> I think it's more than a mere channel ban since the channel itself is merely a day old
[13:32:42] <FireSeraphim> It might be a network ranged ban
[13:33:08] <FireSeraphim> although I will try your suggested command first and see if that generates results
[13:33:26] <Fudge> What ISP are the users connecting from?
[13:33:36] <Fudge> Or, even better, could I have IPs/hostnames?
[13:33:49] <Fudge> I can check to see if there's any ban affecting them, though it's unlikely.
[13:37:22] <Fudge> It could also be an issue with the client they're using
[13:37:42] <Fudge> If you can provide me with logs from their clients' console window, it would also help me
[13:38:01] <Fudge> Clients are disconnected straight away and a reason is displayed if they are banned
[13:38:15] <FireSeraphim> They're mostly using the standard barebones irc client that's available at irc.ircnode.net
[13:38:50] <Fudge> You mean the web client at
http://chat.ircno.de[13:38:51] <Fudge> ?
[13:39:01] <FireSeraphim> yes
[13:39:52] <Fudge> If you could tell the users that are having issues to pastebin what's in the status tab on that client and give it to me, I'd be able to see if there's an issue with actually connecting
[13:40:45] <FireSeraphim> I have already PM Phoenix7786 on the forums, I'm just waiting for him to reply (and yes he is on the forums right now)
[13:41:08] <Fudge> Sure, PM me when you have additional information and I'll look into this for you.
[13:41:19] <FireSeraphim> understood
In essence I cannot help you guys unless you help me by giving me some critical information.