Let's ensure that you're filing for the correct period, Loriat.
When you select a wrong period for filing your tax forms electronically, you'll most likely get errors like this. Kindly close the form that you've prepared and reopen it. On the Select Filing Period section, enter the current date of the form you are filing in the Year field and click OK. Then, try e-filing the WH-1 form again to see if goes through.
In case you get the same error, please give us a call. We can check your filing history to know why QuickBooks keeps telling you it's a duplicate submission.
I'll be around if you need anything else.