No window is appearing in existing SAP scritp form

I was asked to modify the existing SAP script form regarding invoice generation. I can able to see the output through vf02 transaction by mentioning the output type and billing document number but I am not able to see the form in se71. I even enabled 'Graphic form painter' option. Whenever i check this option the window is appearing but with disabled check boxes. How can i see the windows to do the changes?