invalid trigger action statement - can not modify target table

  Explanation:  A trigger action has attempted to modify  (INSERT,
  UPDATE  or  DELETE)  the  table  that is the target of an active
  trigger.  Any table that is  the  target  of  a  trigger  action
  becomes temporarily read-only while the trigger actions execute.

  User Action:  Correct  the  application  logic  to  remove  this
  modify attempt.