I just downloaded the Sitefinity 4 beta for some testing purposes, and am getting a Configuration Error when attempting to browse a recently-created project. The error is:
Could not load file or assembly 'System.Web.Routing, Version=18.104.22.168, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. (C:\Web Sites\Test\web.config line 121)
The .NET 3.5 framework is installed the System.Web assembly appears to be registered correctly.