If you, like me, just downloaded umbraco 7.2 beta 2 to give it a try, unzipped it in a folder to be used by IIS as virtual application or website and browsing to it you get the ASP.net yellow screen of death with such an error:

Could not load file or assembly 'System.Web.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Solution: copy System.Web.Http.dll to the bin folder.

Then you may encounter also:

System.Net.Http.Formatting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Solution: copy System.Net.Http.Formatting.dll to the bin folder.

And finally:

Could not load file or assembly 'System.Web.Http.WebHost, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified.

Solution: copy System.Web.Http.WebHost.dll to the bin folder.

Quick fix, get this umbraco72-beta2-missing-dlls.zip containing System.Web.Http.dll, System.Net.Http.Formatting.dll and System.Web.Http.WebHost.dll

Copy the dlls in the bin folder and enjoy. Don't forget the umbraco permissions, as usual.