The official club statement on www.southendunited.co.uk read: "Paul Robinson has resigned as a Director of the Club because of the demands of his growing legal prctice and his other commitments. As a life long supporter he intends to remain closely involved with the Club."
For once, though you can never be sure with Southend, there doesn't seem to be any particular back story to this, and as far as S24 is aware Paul has never placed any large amounts of money into the club.
Good luck mate.