Looks like the plugin is trying to use an actual "NICKSERV" command, which doesn't work on all IRC networks. Judging from the notice you get, that's likely the case on the server you're trying to use.
You'll have to change the plugin to send a standard message to NickServ instead.
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Re^2: [POE::Component::IRC::Plugin::NickServID] Unable to authenticate,
by three18ti (Scribe) on Dec 28, 2013 at 20:37 UTC