Well, I wouldn't think that any question of liability would arise. There's very little that a parish council must do, as opposed to what it may do.
In this case, the parishioner was too late anyway. The last date for nominations for parish councils in 2015 was 9 April.
With benefit of hindsight, it would have been sensible for the village newsletter to state the closing date for nominations, and to refer to the elections people at the district council, as well as the parish clerk. Things to consider next time!