I'm using MVC 5 and .net 4.6 to create a web API that my mobile app can connect too.

Whenever I build the project I get hundreds of errors telling me that I need to add references that are already there and that literally every type in my project 'does not exist'. Some examples of these errors: (Not including the one in the title)

What I've tried:

• Added a reference to System.Runtime via nuGet. (A recommendation from this question.)
• Removed aspnetcore50 from the frameworks in the project.json file. (Another recommendation, this question.)
• Restarting VS2015, my machine.
• Going through the nuGet package manager and upgrading every package in my project to the latest.
• Actually making sure I can see the references in the references node of the solution explorer.

UPDATE: -My project.json file looks like this. (After modifying based on Karls answer. The error list is now down to ten, however they are still the same errors as before.)

{
  "commands": {
    "web": "Microsoft.AspNet.Hosting --server Microsoft.AspNet.Server.WebListener --server.urls http://localhost:5000"
  },
  "dependencies": {
    "Microsoft.AspNet.Server.IIS": "1.0.0-beta5",
    "Microsoft.AspNet.Server.WebListener": "1.0.0-beta5",
    "Microsoft.AspNet.Diagnostics": "1.0.0-beta5",
    "Microsoft.AspNet.Mvc": "6.0.0-beta5",
    "System.Runtime": "4.0.20-beta-23019"
  },
  "exclude": [
    "wwwroot",
    "node_modules",
    "bower_components"
  ],
  "frameworks": {
    "dnx451": {
      "frameworkAssemblies": {
        "System.Data": "4.0.0.0",
        "System.Data.DataSetExtensions": "4.0.0.0",
        "System.Data.Linq": "4.0.0.0"
      }
    }
  },
  "publishExclude": [
    "node_modules",
    "bower_components",
    "**.xproj",
    "**.user",
    "**.vspscc"
  ],
  "version": "1.0.0-*",
  "webroot": "wwwroot"
}