Immobiliser kicks in wont always disengage when fob is used?

occasionally when I go to my car it won't start wont turn over no lights on dash which should'nt be lock and unlock using fob still wont start but if I use key in door and lock and unlock will usually start is this the immobiliser or something else help!!!! Vauz Zafira 1.6 club 06 plate - doesnt do this all the time