The type or namespace name 'Linq' does not exist in the namespace 'System'

Questions
1

When installing Umbraco from the web platform installer, the following error occurs when I go to the install/default.aspx page from the installer.

Compiler Error Message: CS0234: The type or namespace name 'Linq' does not exist in the namespace 'System' (are you missing an assembly reference?)

Source Error:

  
Line 1:  using System;
Line 2:  using System.Linq;
Line 3:  using System.Data.Linq;
Line 4:  using System.Data.Linq.Mapping;

Source File: d:\Websites\app_code\Test.cs    Line: 2

This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/8650-the-type-or-namespace-name-linq-does-not-exist-in-the-namespace-system