Cannot Force Close PO

Hi Experts,

I wish to close PO but unfortunately I am getting errors. Can you please advise how? As a background, these PO's are obsolete PO's. and related documents attached to these PO's has likewise been deleted or no longer existing (eg, Invoice, Sales document, etc). Therefore, i just want that these PO's will no longer show in any Open PO reports.

Now I have tried to tick Delivery indicator for these PO's but it seems any changes to these will have errors and no longer possible to save the PO.

Thanks in advance.