I had the same problem, here is how I solved it:
Next to the installed Visio MS SQL Server drivers, SQL Server Native 10.0 is marked at the bottom of the list
In the "Data Sources" section, click "New" (I used the "Custom Data Source"), then on the "Create a New Data Source" screen I used SQL Server Native 10.0
Upon completion of the wizard, a data source has appeared.
The main thing is that SQL Server 10.0 is installed next to the Microsoft SQL Server option (not checked by default)
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