HtmlString only exists in ASP.NET 4. MvcHtmlString was a compatibility shim added to MVC 2 to support both .NET 3.5 and .NET 4. Now that MVC 3 is .NET 4 only, it’s a fairly trivial subclass of HtmlString presumably for MVC 2->3 for source compatibility. If you’re ever going to drop back to MVC 2 … Read more
ASP.NET 4 was not registered in IIS. Had to run the following command in the command line/run 32bit (x86) Windows %windir%\Microsoft.NET\Framework\v4.0.30319\aspnet_regiis.exe -ir 64bit (x64) Windows %windir%\Microsoft.NET\Framework64\v4.0.30319\aspnet_regiis.exe -ir Note from David Murdoch’s comment: That the .net version has changed since this Answer was posted. Check which version of the framework is in the %windir%\Microsoft.NET\Framework64 directory and … Read more