Edit permission to Vendor packing slip form ?

Hi,

I am trying edit values in vendor packing slip form ie 'vendpackingslipjour' after doing packing slip of po. I set the form datasource table property as Allow edit: Yes for vendpackingslipjour  Data source and tryied using code. But I am unable to edit still. Is there any security permission to be done? I have admin rights.

Thanks,

Santhosh