I’ve created a new scheme based on my current app.config to get the messages to disappear.
I just used the button in Visual Studio that says “Create Schema” and an xsd schema was created for me.
Save the schema in an apropriate place and see the “Properties” tab of the app.config file where there is a property named Schemas. If you click the change button there you can select to use both the original dotnetconfig schema and your own newly created one.