Error when confirm Purchase Order

Hi Experts,

I got an error message when confirm purchase order

The error message is 

"Cannot edit a record in Source document line (SourceDocumentLine). The record has never been selected."

Strangely only the PO number can not confirm. The other Purchase order can confirm.

I've follow all the way in this forum and still the same.

For your information it's generated by subcontracted production order..

Thanks and regards

Mulyadi