One or more types required to compile a dynamic expression cannot be found. Are you missing references to Microsoft.CSharp.dll and System.Core.dll?

On your solution explorer window, right click to References, select Add Reference, go to .NET tab, find and add Microsoft.CSharp.

Alternatively add the Microsoft.CSharp NuGet package.

Install-Package Microsoft.CSharp

Make sure that your project is targeting the .NET framework 4.0. Visual Studio 2010 supports .NET 3.5 framework target also, but .NET 3.5 does not support the dynamic keyword.

You can adjust the framework version in the project properties. See http://msdn.microsoft.com/en-us/library/bb398202.aspx for more info.

I had the same issue except removing and adding the reference back did not fix the error, so I changed .Net version from 4.5 to 4.5.1.

To achieve this go to your web.config file and change the following lines

<compilation debug="true" targetFramework="4.5" />
<httpRuntime targetFramework="4.5" />

to this

<compilation debug="true" targetFramework="4.5.1" />
<httpRuntime targetFramework="4.5.1" />

and rebuild.