Comment by thaumasiotes

It would mean that somewhere in your sentence there's a clause headed by a passive verb. A finite verb is one that heads a clause.

This terminology is where we get the name of the "infinitive" form from, by the way.

As a rule of thumb, the nonfinite forms of a verb are its infinitives and participles. jcranmer used a passive participle, but all of his clauses are active. Unnoticed doesn't have a clause around it.

(He might have thought that go unnoticed is a passive form, perhaps of the verb notice (?), in which case that would just be an error.)