trigger can not be invoked - it is marked invalid

  Explanation:  This trigger can not  be  invoked.   It  has  been
  marked  invalid  as  a  result  of  a  data  definition language
  operation on an object upon which  this  trigger  was  dependent
  (with language semantics dependency).

  User Action:  The trigger must be dropped and redefined so  that
  it inherits the updated schema.