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1. Find and Delete the duplicate document
   Note: This should be done using the Delete Invoices button on the Workflow tab.
   1. Query back all documents with the relevant vendor and Invoice ID
   2. Once you find what portion of workflow the duplicate documents are in, navigate workflow tab.
   3. Find the document in the list of Life Cycles
   4. Delete using the "Delete Invoices" Button
      
2. Allow duplicate Invoices on the Control Form 
   1. Navigate to the Work Flow view
      
   2. Select/Expand the "AP01 - Control Forms" menu item
   3. Select the "AP01 - Active Forms" sub item
      
   4. Select the Control form for the relevant Organizational Unit in AP01 - Active Forms
   5. Uncheck check the "Allow Duplicate Invoices" box
      
      
   6. Save the changes made to the control formControl Form
   7. Click on 'UPDATE PENTA' Ad Hoc Task to update the Database before resubmitting the Routing Form.

Cause 

When checking for duplicate invoices OnBase does not look at Penta, rather it checks all existing documents in workflow (across all users). In other words if you are seeing that error it means another document exists in OnBase with that Vendor and Invoice #.