Forms personalizaiton not working to make the fields mandatory

Hi all,
      We need to make job and grade field mandatory in assignment screen.

      I did but it is not working. It is saving without a value in the mandatory field.

      Used WHEN_NEW_FORM_INSTANCE..
           PROPERTY --> OBJECT : ITEM
                        TARGET OBJECT : ASSGT.GRADE_NAME
                        PROPERTY NAME : REQUIRED
                        VALUE   : TRUE.

 
Thanks