Received a negative inventory quantity against PO when sent product back to vendor.  Received credit memo from vendor.  Keyed negative info.  Discovered I made a typo in the invoice.  Went back in to AP-C and typed PO # and invoice number again.  Answered 'YES' to question 'Invoice number: XXX already exists for this Vendor.  Would you like to reverse it?'
 
Get error message: 'Details required to reverse this invoice cannot be found.'
 
Any ideas why this is not working.  I just posted the invoice a few minutes ago, discovered the error, and tried to reverse it so it's not been out there for weeks or something.  I even posted all GL transactions to the GL in case that had something to do with it.  Same result.
 
Thanks!

You may want to check if purchase order status is closed - which may be preventing the change.
 
If status is closed, re-open purchase order by going to PO_D, View PO receivers, find purchase order and select button on bottom of screen to reopen po.
 
Try again to see if you can edit the voucher.