I have recently updated EntityFramework in my WebAPI project from v5 to v6. Unfortunately it seems like somewhere, somehow, there is a reference that exists in some config s
Keeping the same entityFramework versions in both parent and virtual folder web configs fixes the issue for me.
If you have an older version of the entityFramework installed in the project, right click on the project then go to "Manage NuGet Packages" and then select "search online" option from the left and select version you want and install it.