Missing a using directive or an assembly reference:
An error describe that you are simply missing a specific namespace or assembly reference and will just need to add in your project. You can use a package manager in Dot. Net Framework 4.5 that describe below:
NuGet Package Manager: is a collection of tools that automate the process of downloading, installing, upgrading, configuring, and removing packages from a VS Project
NuGet requires that PowerShell 2.0 be installed on system. PowerShell 2.0 is already installed on Windows 7 and Windows Server 2008 R2.
NuGet package manager is rich as it automatically brought down assemblies into your machine, a reference is added into your project and everything it needs is merged non-destructively into web.config.
You can use NuGut by going to Tools Menu >>>> Library Package Manager >>>> Manager NuGut packages for solutions