Grab the recommended 4.0 download from https://compositec1.codeplex.com/releases and copy the System.Web:*.dll from it (folder /Website/Bin) to your local websites bin directory.
We will look into having those DLLs already in place in the source version - sorry for the inconvenience.
We will look into having those DLLs already in place in the source version - sorry for the inconvenience.