vs 2012 - The primary reference could not be resolved because it has an indirect dependency on the framework assembly

I started getting this error after changing the target framework in build configuration for my web application in Visual Studio 2012.

To resolve this I had to unload the project and reload it into the solution.Right Click on the application in VS 2012 solution and select Unload Project in the context menu.

Reload the project by right clicking on the project that is not available