ASP.NET MVC / IIS 7.5: 500 Internal Server Error for static content only

Question

An ASP.NET MVC project running under IIS 7.5 (but problem may exist on earlier versions and non-MVC sites) which was previously working has started returning 500 Internal Server

Answer 1

Always remove any mimetype you want to add, just in case it's already defined at the IIS/server level, eg: