Editing Lines on Purchase Orders throwing error "Items on this line have been received. If you wish to delete the line, you must first delete the corresponding line(s) in the associated transaction(s)."

This message is encountered when:

1.    The purchase order line item has been received; and/or

2.    The purchase order line item has been billed.

To be able to edit the line item:

1.     The line item in the corresponding item receipt should be removed.

2.     The line item in the corresponding bill should be removed.

Such error don't unlink records.