Cannot update approval template/approval stages

Hi,

Using SAP Business One 9.0 (9.00.061) PL: 08 HOTFIX1 (32-bit)

Created PO Approval template name 'PO Approval', it been used for some time and now customer want to change authorize person.

When try to update the approval stages, sysem prompted: Cannot update approval stage; existing authorization processes are based on current stage

l have logged in using superuser and checked:

1. No outstanding PO pending for approval

2. All approved PO had been added

3. No open draft PO

Refer print screen attached.

Any idea?