How to Undo Changes to a Re-opened Closed PO Line for OSP Item

User mistakenly re-opened a closed PO line for an OSP item.  Because of this, the PO's status changed back to 'Requires Reapproval'.  She cannot re-approve the PO nor close/cancel the re-opened line.  The only option available for the line is Cancel.  There is no option to Close.  When she tries to cancel the line, she gets the error: "Please undo the changes to the document in the current revision before taking the cancel action.  Cause: You are trying to cancel a document that has been altered since its last archived revision.  Action: You must first undo the changes before you can cancel the document."