Could not load file or assembly 'System.Web.Http 4.0.0 after update from 2012 to 2013

Question

I did the upgrade according to. http://www.asp.net/mvc/tutorials/mvc-5/how-to-upgrade-an-aspnet-mvc-4-and-web-api-project-to-aspnet-mvc-5-and-web-api-2

I get the er

Answer 1

I had the same problem with System.Web.Http.WebHost, Version=5.2.6.0 being referenced but the latest NuGet package was 5.2.7.0. I edited the web.config files, re-installed the NuGet package, then edited the visual studio project files for all of my projects to make sure no references to 5.2.6.0 persisted. Even after all this, the problem persisted.

Then I looked in the bin folder for the project that was throwing the exception, where I found a DLL for one of my other projects that is not a dependency and should never have been there. I deleted the offending DLL (which had been compiled using the 5.2.6.0 version of System.Web.Http.WebHost), rebuilt the troublesome project, and now it is working.