The located assembly's manifest definition does not match the assembly reference

Question

I am trying to run some unit tests in a C# Windows Forms application (Visual Studio 2005), and I get the following error:

System.IO.FileLoadException: Co

Answer 1

I added a NuGet package, only to realize a black-box portion of my application was referencing an older version of the library.

I removed the package and referenced the older version's static DLL file, but the web.config file was never updated from:

to what it should have reverted to when I uninstalled the package: