After a number of 500 errors coming up from IIS8 under Windows Server 2012, I final found the solution.

The solution was to go back to the Microsoft Server 2012 Dashboard and select the “Add Roles” feature. Scroll down to the root “Web Server (IIS)”, expand “Web Server”, expand “Application Development” and select “ASP.NET 3.5” and “ASP.NET 4.5” and “Install”.

What confused me originally was I hadn’t expanded “Application Development”, but selected IIS and continued. On the next step, “Features”, “.NET Framework 4.5 Features” was selected by default so I selected “.NET Framework 3.5 Features” and thought all would be fine.