How to resolve: "Unrecognized attribute ‘targetFramework’. Note that attribute names are case-sensitive"

I was getting the error "Unrecognized attribute ‘targetFramework’. Note that attribute names are case-sensitive" on an ASP .NET 4.0 website. This was caused by the application pool targeting the wrong .net framework, change the application pool to the correct .net framework and the error will be resolved.

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