Could not load file or assembly System.Web.Mvc or one of its dependencies

Question

currently working on asp.net mvc5 (old mvc3 project). It builds just fine, but when I start the project but when I run the project I am facing the following error.

Answer 1

Could you post your web.config file here?. It seems that you opened a mvc3 project in a newer environment and the migrating function of your IDE (i.e. Visual Studio) doesn't work well. The versions of System.Web.Mvc.DLL are mismatched (in config file and the one in bin/ directory). There are two ways to solve this: 1. Modify the version of System.Web.Mvc package/assembly in the config file. 2. Copy System.Web.Mvc.dll from your old project to the new project (bin/ folder).

I had faced the similar issue for other .dll files before. At that time, I chose to delete all .dll files and use NuGet Package Manager to download them again.