A brief explanation of the “Unable to connect (Can’t assign requested address)” error.
Due to the DoS attacks against DALnet, the DALnet administration disabled their random irc.dal.net server alias. This used to resolve to a list of one or more real server IP numbers, but often these days it points to 255.255.255.255 which is not a real IP. You can see this for yourself using mIRC’s /dns feature: /dns irc.dal.net
When you try to connect to that bogus IP, mIRC gives the aforementioned error. The only way to connect is to use a specific server name like irc.example.com using the tips on the main DALnet connection guide page: http://irchelp.org/dalnet
Why did they do this? If there is no publicly addressable (i.e., “real”) IP number, then there is no target for the DoS attackers. Unfortunately, that also means there is no way for legitimate users to connect either. This applies to nearly all of the servers shown in the /links list, even after you manage to connect do DALnet. The automatic server list in the URL above checks this for you, so you can tell which servers are “real” and which are not accessible.