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

When trying to deploy my WCF service.
I was getting the error “Unrecognized attribute ‘targetFramework’. Note that attribute names are case-sensitive” on an ASP .NET 4.0 website.

I first thought that this was happening because .NET 4 was not on the server, but even after installing .NET 4 the problem persisted.

The error was caused by the application pool targeting the wrong .net framework.

To resolve the problem : Change the application pool to the correct .net framework and the error will be resolved.