You must add a reference to assembly mscorlib, version=4.0.0

51
votes

I'm having some trouble migrating a web project from RC1 to RC2. When I switched, I'm getting a bunch of these errors throughout the project.

The type 'Func<,>' is defined in an assembly that is not referenced. You must add a reference to assembly 'mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

Looks like all of the linq functions and lambda expressions are not working.

This is what my project.json file looks like:

  "frameworks": {
    "netcoreapp1.0": {
      "dependencies": {
        "System.Linq": "4.1.0-rc2-24027"
      },
      "imports": [ "net451", "portable-net45+win8" ]
    }
  },
  "dependencies": {
    "NETStandard.Library": "1.5.0-rc2-24027",
    "Microsoft.EntityFrameworkCore": "1.0.0-rc2-final",
    "Microsoft.EntityFrameworkCore.SqlServer": "1.0.0-rc2-final",
    "System.ComponentModel.Annotations": "4.1.0-*"
  }

Any ideas what this means? I've tried running dotnet restore, did not help.

6
c#linqasp.net-core.net-core
I can't reproduce this error. Could you share your whole project.json? - svick
I've encountered similar issues when using the imports argument. Try removing it entirely or changing net451 to dnx451 - Negorath
@Negorath good idea, also consider looking at what is added in a new RC2 web application. The imports section is "dotnet5.6", "dnxcore50", "portable-net45+win8" - wal

6 Answers

80
votes

I had the same issue and adding the following package to my project.json dependencies fixed it for me: 

"Microsoft.NETCore.Portable.Compatibility": "1.0.1-rc2-24027",

This package enables compatibility with mscorlib-based PCLs.

41
votes

In fact, the problem is an old lib that requires an asp.net 4.0 or 4.5 vesion (less than Core).

Microsoft provides a solution for it by installing the fallowing NuGet package.

Microsoft.NETCore.Portable.Compatibility

this way you will be able to run your code with old libs.

4
votes

I got this error when I created a new project using the template Class Library (.NET Standard) and ported some code into it that I wanted to re-use.

I created a new project Class Library (.NET Framework) and moved the code there instead and it worked without any issues.

2
votes

Delete the .csproj.user as per in the Screenshot present in the solution folder. Unload the project from solution explorer. Reload the project and build it once. This worked for me.

0
votes

I don't have the rep to comment but Matt Kemp's post lead to my solution . In my case it was using a Class Library(.Net Standard) instead of Android Class Library (Xamarin)

0
votes

mscorlib reference is added by default, but it seems to be a visual studio reference issue. I have deleted my project and created new one then it worked fine.