The 'Forward' check box is not accessible on Approve PO form

Hi,

we are using Position Hierarchy. When any user creates the PO and click on Approve button the 'Forward' (just below the Submit for Approval checkbox) check box on Approve Document window is not accessible.

In Standard Purchase Order Document Type, we have done below setups

Can Change Forward-To - Checked

Can Change Approval Hierarchy - Checked

but still Forward check box is not accessible.

Thanks,

Nilesh