You must add a reference to assembly netstandard Version 2 0 0 0

Question

The project is an ASP NET MVC Web App targeting the  NET Framework 4 6 1   All of a sudden  some NuGet packages were upgraded  I started to get the following error during runtime      CS0012  The type  System Object  is defined in an assembly that is not   referenced  You must add a reference to assembly  netstandard    Version 2 0 0 0  Culture neutral  PublicKeyToken cc7b13ffcd2ddd51     In my main view Index cshtml  in a line where I make use of  Html ActionLink  I do have  NET Core SDK 2 0 and  NET Framework 4 7 1 installed in my machine but I don t want to include a reference to it  This is a  NET Framework web app only  it s hosted on Windows IIS where the installed framework is 4 6 1  there s no NET Core installed in the server   So why is it asking to add a reference to netstandard  How can I fix it without referencing netstandard but the full Windows  NET Framework 4 6 1   I ve checked out a previous commit which worked fine and I m still getting this error  So it s not related to NuGet packages being upgraded  Seems to be something on my local dev machine   If a publish the app to a directory and run it with IIS it works   Link to  csproj gist  packages config   lt  xml version  1 0  encoding  utf-8   gt   lt packages gt     lt package id  Antlr  version  3 5 0 2  targetFramework  net46    gt     lt package id  BundleTransformer Core  version  1 9 69  targetFramework  net46    gt     lt package id  BundleTransformer Handlebars  version  1 9 73  targetFramework  net46    gt     lt package id  BundleTransformer Less  version  1 9 69  targetFramework  net46    gt     lt package id  BundleTransformer Yui  version  1 9 52  targetFramework  net46    gt     lt package id  Dapper  version  1 42  targetFramework  net46    gt     lt package id  EcmaScript Net  version  1 0 1 0  targetFramework  net46    gt     lt package id  EntityFramework  version  6 0 0  targetFramework  net46    gt     lt package id  Glimpse  version  1 8 6  targetFramework  net46    gt     lt package id  Glimpse AspNet  version  1 9 2  targetFramework  net46    gt     lt package id  Glimpse Mvc5  version  1 5 3  targetFramework  net46    gt     lt package id  JavaScriptEngineSwitcher Core  version  1 2 4  targetFramework  net46    gt     lt package id  JavaScriptEngineSwitcher V8  version  1 3 0  targetFramework  net46    gt     lt package id  jQuery  version  2 1 3  targetFramework  net46    gt     lt package id  jQuery Validation  version  1 13 1  targetFramework  net46    gt     lt package id  LowercaseDashedRoute  version  1 0 14  targetFramework  net46    gt     lt package id  Microsoft AspNet Mvc  version  5 2 3  targetFramework  net46    gt     lt package id  Microsoft AspNet Razor  version  3 2 3  targetFramework  net46    gt     lt package id  Microsoft AspNet Web Optimization  version  1 1 3  targetFramework  net46    gt     lt package id  Microsoft AspNet WebApi  version  5 2 3  targetFramework  net46    gt     lt package id  Microsoft AspNet WebApi Client  version  5 2 3  targetFramework  net46    gt     lt package id  Microsoft AspNet WebApi Core  version  5 2 3  targetFramework  net46    gt     lt package id  Microsoft AspNet WebApi WebHost  version  5 2 3  targetFramework  net46    gt     lt package id  Microsoft AspNet WebPages  version  3 2 3  targetFramework  net46    gt     lt package id  Microsoft jQuery Unobtrusive Validation  version  3 2 3  targetFramework  net46    gt     lt package id  Microsoft Owin  version  3 0 1  targetFramework  net46    gt     lt package id  Microsoft Owin Host SystemWeb  version  3 0 1  targetFramework  net46    gt     lt package id  Microsoft SqlServer Compact  version  4 0 8876 1  targetFramework  net46    gt     lt package id  Microsoft Web Infrastructure  version  1 0 0 0  targetFramework  net46    gt     lt package id  Moment js  version  2 10 2  targetFramework  net46    gt     lt package id  Newtonsoft Json  version  10 0 3  targetFramework  net46    gt     lt package id  NWebsec  version  5 1 1  targetFramework  net46    gt     lt package id  NWebsec Core  version  2 1 0  targetFramework  net46    gt     lt package id  NWebsec Mvc  version  5 1 1  targetFramework  net46    gt     lt package id  Owin  version  1 0  targetFramework  net46    gt     lt package id  Respond  version  1 4 2  targetFramework  net46    gt     lt package id  Sendgrid  version  6 3 0  targetFramework  net46    gt     lt package id  SendGrid SmtpApi  version  1 3 1  targetFramework  net46    gt     lt package id  Serilog  version  2 6 0  targetFramework  net46    gt     lt package id  Serilog Enrichers Environment  version  2 1 2  targetFramework  net46    gt     lt package id  Serilog Sinks File  version  3 2 0  targetFramework  net46    gt     lt package id  Serilog Sinks RollingFile  version  3 3 0  targetFramework  net46    gt     lt package id  Serilog Sinks Sentry  version  2 1 4  targetFramework  net46    gt     lt package id  SerilogWeb Classic  version  2 1 17  targetFramework  net46    gt     lt package id  SharpRaven  version  2 2 0  targetFramework  net46    gt     lt package id  System Data SQLite  version  1 0 108 0  targetFramework  net46    gt     lt package id  System Data SQLite Core  version  1 0 108 0  targetFramework  net46    gt     lt package id  System Data SQLite EF6  version  1 0 108 0  targetFramework  net46    gt     lt package id  System Data SQLite Linq  version  1 0 108 0  targetFramework  net46    gt     lt package id  Twitter Bootstrap Less  version  3 3 4  targetFramework  net46    gt     lt package id  WebActivatorEx  version  2 0 6  targetFramework  net46    gt     lt package id  WebGrease  version  1 6 0  targetFramework  net46    gt     lt package id  YUICompressor NET  version  2 7 0 0  targetFramework  net46    gt   lt  packages gt    When publishing the app using VS2017 to the file system I get the following warning in the output      The following assembly has dependencies on a version of the  NET   Framework that is higher than the target and might not load correctly   during runtime causing a failure  netstandard  Version 2 0 0 0    Culture neutral  PublicKeyToken cc7b13ffcd2ddd51  The dependencies   are  System Transactions  Version 4 0 0 0  Culture neutral    PublicKeyToken b77a5c561934e089  You should either ensure that the   dependent assembly is correct for the target framework  or ensure that   the target framework you are addressing is that of the dependent   assembly    But I can t find anything on System Transactions  How can I search what s referencing it

User · Accepted Answer

I think the solution might be this issue on GitHub:

Try add netstandard reference in web.config like this:"

<system.web>
  <compilation debug="true" targetFramework="4.7.1" >
    <assemblies>
      <add assembly="netstandard, Version=2.0.0.0, Culture=neutral, 
            PublicKeyToken=cc7b13ffcd2ddd51"/>
    </assemblies>
  </compilation>
  <httpRuntime targetFramework="4.7.1" />

I realise you're using 4.6.1 but the choice of .NET 4.7.1 is significant as older Framework versions are not fully compatible with .NET Standard 2.0.

I know this from painful experience, when I introduced .NET Standard libraries I had a lot of issues with NUGET packages and references breaking. The other change you need to consider is upgrading to PackageReferences instead of package.config files.

See this guide and you might also want a tool to help the upgrade. It does require a late VS 15.7 version though.

User · Answer

Manually editing the  csproj file and adding the reference below worked for me    lt Reference Include  netstandard    gt    Thank you to Fahad Alshaya who suggested it here

User · Answer

I had to do a combination of other people s answers on this thread     Install the NetStandard Library via NuGet Manually editing the  csproj file and adding the reference   lt Reference Include  netstandard    gt  Expanding project-- References in the VS Solution Explorer  right clicking on  netstandard  and showing the properties page and setting  Copy Local  to true

User · Answer

Deleting Bin and Obj folders worked for me

User · Answer

After upgrading from 4 6 1 framework to 4 7 2 we started getting this error    The type  System Object  is defined in an assembly that is not referenced  You must add a reference to assembly  netstandard  Version 2 0 0 0  Culture neutral  PublicKeyToken cc7b13ffcd2ddd51    and ultimately the solution was to add the  netstandard  assembly reference mentioned above    lt compilation debug  true  targetFramework  4 7 1   gt       lt assemblies gt         lt add assembly  netstandard  Version 2 0 0 0  Culture neutral               PublicKeyToken cc7b13ffcd2ddd51   gt       lt  assemblies gt     lt  compilation gt

User · Answer

I have run into this before and trying a number of things has fixed it for me:

Delete a bin folder if it exists
Delete the hidden .vs folder
Make sure the 4.6.1 targeting pack is installed
Last Ditch Effort: Add a reference to System.Runtime (right click project -> add -> reference -> tick the box next to System.Runtime), although I think I've always figured out one of the above has solved it instead of doing this.

Also, if this is a .net core app running on the full framework, I've found you have to include a global.json file at the root of your project and point it to the SDK you want to use for that project:

{
  "sdk": {
    "version": "1.0.0-preview2-003121"
  }
}

User · Answer

We started getting this error on the production server after deploying the application migrated from 4.6.1 to 4.7.2.

We noticed that the .NET framework 4.7.2 was not installed there. In order to solve this issue we did the following steps:

Installed the .NET Framework 4.7.2 from:

https://support.microsoft.com/en-us/help/4054530/microsoft-net-framework-4-7-2-offline-installer-for-windows
Restarted the machine
Confirmed the .NET Framework version with the help of How do I find the .NET version?

Running the application again with the .Net Framework 4.7.2 version installed on the machine fixed the issue.

User · Answer

Might have todo with one of these    Install a newer SDK  In  csproj check for Reference Include  netstandard   Check the assembly versions in the compilation tags in the Views Web config and Web config

User · Answer

Although this is an old thread  I had the same issue today  last week I updated some NuGet packages and although the MVC website worked OK on my dev machine when I published to the testing server it failed   I read numerous posts but none worked  I finally compared the DLL s in my local bin to those in the testing server and found that the netstandard dll was not uploaded  once uploaded the website worked OK  not sure why VS2017 web deploy did not publish the DLL   Just something to look out for in case none of the above work for you

User · Answer

I experienced this when upgrading  NET Core 1 1 to 2 1   I followed the instructions outlined here   Try to remove  lt RuntimeFrameworkVersion gt 1 1 1 lt  RuntimeFrameworkVersion gt  or  lt NetStandardImplicitPackageVersion gt  section in the  csproj

User · Answer

The solution of Quango in  is working but I prefer to resolve it by adding this code in my Web config like new projects    lt system codedom gt       lt compilers gt         lt compiler language  quot c  cs csharp quot  extension  quot  cs quot          type  quot Microsoft CodeDom Providers DotNetCompilerPlatform CSharpCodeProvider  Microsoft CodeDom Providers DotNetCompilerPlatform  Version 3 6 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35 quot          warningLevel  quot 4 quot  compilerOptions  quot  langversion default  nowarn 1659 1699 1701 quot   gt         lt compiler language  quot vb vbs visualbasic vbscript quot  extension  quot  vb quot          type  quot Microsoft CodeDom Providers DotNetCompilerPlatform VBCodeProvider  Microsoft CodeDom Providers DotNetCompilerPlatform  Version 3 6 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35 quot          warningLevel  quot 4 quot  compilerOptions  quot  langversion default  nowarn 41008  define  MYTYPE   amp quot Web  amp quot   optionInfer  quot   gt       lt  compilers gt     lt  system codedom gt

User · Answer

Those who are not having web config file  Output Type other than web application  update the project file   csproj  with below give code  It may cause due to adding removing the  netframework in improper way or it may broke unexpected way     lt ItemGroup gt       lt Reference Include  quot netstandard quot    gt     lt  ItemGroup gt   Output Type  Console application Class Library

User · Answer

I am facing Same Problem i do following Setup Now Application Work fine

1-

<compilation debug="true" targetFramework="4.7.1">
      <assemblies>
        <add assembly="netstandard, Version=2.0.0.0, Culture=neutral, 
      PublicKeyToken=cc7b13ffcd2ddd51"/>
      </assemblies>
    </compilation>

2- Add Reference

 **C:\Program Files (x86)\Microsoft Visual
Studio\2017\Professional\Common7\IDE\Extensions\Microsoft\ADL
 Tools\2.4.0000.0\ASALocalRun\netstandard.dll**

3-

Copy Above Path Dll to Application Bin Folder on web server

User · Answer

I was facing this problem when trying to add a .NETStandard dependency to a .NET4.6.1 library, and compiling it in Linux with Mono 4.6.2 (the version that comes with Ubuntu 16.04).

I finally solved it today; the solution requires to do both of these things:

Change <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion> to <TargetFrameworkVersion>v4.7.1</TargetFrameworkVersion> in the .csproj file.
Upgrade your mono to a newer version. I believe 5.x should work, but to be sure, you can just install Ubuntu 20.04 (which at the time of writing is only in preview), which includes Mono 6.8.0.105.

User · Answer

Set Copy Enbale to true in netstandard dll properties  Open Solution Explorer and right click on netstandard dll  Set Copy Local to true

User · Answer

You can add  to your web config in your project   It wouldn t work when you add it to projects web config because it works with MVC

User · Answer

This is where netstandard dll exists  C  Program Files  x86  Reference Assemblies Microsoft Framework NETFramework v4 7 2 Facades netstandard dll Add ref to your Project through this

User · Answer

This issue is based on your installed version of visual studio and Windows, you can follow the following steps:-

Go to Command Window

downgraded your PCL by the following command

Install-Package Xamarin.Forms -Version 2.5.1.527436

Rebuild Your Project.
Now You will able to see the required output

[asp.net] You must add a reference to assembly 'netstandard, Version=2.0.0.0

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