Description & Cause
When trying to open QuickBooks and/or run the QuickBooks Web Connector as "administrator" or in compatibility mode, you may encounter this error. In addition, if you are attempting to add a QWC pairing file, QuickBooks will open another instance, triggering this error.
Right click QuickBooks on your task bar:
Make sure compatibility mode and run this program as administrator are unchecked:
Open your web connector and do the same thing: