您必须添加对程序集 mscorlib 的引用，版本=4.0.0

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

For MVC 5, you must add 2 references Right click the project, and add reference

Assemblies > Framework

Add this 2 references

• System.IdentityModel 4.0.0.0
• System.IdentityModel.Services 4.0.0.0

Answer 6

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)

Answer 7

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.

Answer 8

I had this error all of a sudden while working in a unit test project. Tried the suggestions as mentioned before like unloading and reloading the project, rebuild etc. Eventually all it took was a restart of Visual Studio - Did you try to turn it off and on again :-) VS version 16.11.5

Answer 9

Adding this here in the hopes it'll help someone else, though my scenario was not a web project. When loading a winforms form (designer) I was getting the error Unable to find assembly 'mscorlib I deleted that file's resx file and let the designer re created it. This happened after copying a form that was created in a .netframework project to a .net6 project.

Again, not related to the OP but this was the closest SO thread I could find to my problem