The type or namespace name System could not be found

Question

I have the following errors  and more  in all my views    cshtml  when opening my project in Visual Studio 2015 Professional      Error  CS0246  The type or namespace name  System  could not be found  are you missing a using directive or an assembly reference     Severity    Code    Description Project File    Line      Error  CS0518  Predefined type  System Object  is not defined or imported   Severity    Code    Description Project File    Line      Error  CS0518  Predefined type  System String  is not defined or imported   I got these references    lt ItemGroup gt   lt Reference Include  Microsoft CSharp    gt   lt Reference Include  Sitecore Kernel  Version 7 0 0 0  Culture neutral  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX Sitecore Kernel dll lt  HintPath gt   lt  Reference gt   lt Reference Include  Sitecore Mvc  gt     lt HintPath gt N  XXX Sitecore Mvc dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web DynamicData    gt   lt Reference Include  System Web Entity    gt   lt Reference Include  System Web ApplicationServices    gt   lt Reference Include  System ComponentModel DataAnnotations    gt   lt Reference Include  System    gt   lt Reference Include  System Data    gt   lt Reference Include  System Core    gt   lt Reference Include  System Data DataSetExtensions    gt   lt Reference Include  System Web Extensions    gt   lt Reference Include  System Web Helpers  Version 2 0 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX System Web Helpers dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web Mvc  Version 4 0 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX System Web Mvc dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web Providers  gt     lt HintPath gt N  XXX System Web Providers dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web Razor  Version 2 0 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX System Web Razor dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web WebPages  Version 2 0 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX System Web WebPages dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web WebPages Deployment  Version 2 0 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX System Web WebPages Deployment dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Web WebPages Razor  Version 2 0 0 0  Culture neutral  PublicKeyToken 31bf3856ad364e35  processorArchitecture MSIL  gt     lt SpecificVersion gt False lt  SpecificVersion gt     lt HintPath gt N  XXX System Web WebPages Razor dll lt  HintPath gt   lt  Reference gt   lt Reference Include  System Xml Linq    gt   lt Reference Include  System Drawing    gt   lt Reference Include  System Web    gt   lt Reference Include  System Xml    gt   lt Reference Include  System Configuration    gt   lt Reference Include  System Web Services    gt   lt Reference Include  System EnterpriseServices    gt      I found some solutions saying that a mscorlib wasn t referenced   but when I tried to add it it sayd that it s already there  even though I don t see it on the csproj file    System dll reference       SOLUTION    Managed the issue   I had the build path set to a  c     bin  instead of   bin   I believe this happened because I don t have any web config in the root of the project  so VS didn t identify my project as a web project

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Unload project - gt  Reload project normally fixes this weird  Nuget related  error to me

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Follow these steps    right click on Solution  gt  Restore NuGet packages right click on Solution  gt  Clean Solution right click on Solution  gt  Build Solution Close Visual Studio and re-open  Rebuild solution  If these steps don t initially resolve your issue try repeating the steps a second time   Thats All

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right click you project name then open the properties windows  downgrade your Target framework version  build Solution  then upgrade your Target framework version to the latest  build Solution

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For me it only happened in one project and I tried everything I found online and nothing seemed to help  I was ready to delete and recreate the project when after messing through the projects properties changing the  NET framework target from 4 7 2 to 4 8 fixed the issue  I changed it back to 4 7 2 later and the error is gone  Hopefully this helps other users as well

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Using VS Professional 2019  I was trying to run a downloaded solution from a Udemy class on selenium automation testing  and most of the projects had errors in the project references sections  I tried cleaning  rebuilding  closing VS  Then  in VS  when I right clicked on the solution in Solution Explorer and chose Manage Nuget Packages for Solution  there were 2 available updates  for MSTest TestAdapter and MSTest TestFramework  and when I installed those  the error messages on the references for all the projects went away  for the references to those  as well as for the references to System and System Core

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If cleaning the solution didn t work and for anybody who see s this question and tried moving a project or renaming   Open Package manager console and type  dotnet restore

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I had the same problem earlier when I tried to edit an open source project from the internet     Solved it by just Cleaning the solution and rebuilding it    Hope this helps

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I had to delete the bin and obj folders from each folder in order to resolve this

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I attempted to re-create your issue and came up with a similar error when the solution was created in visual studio 2013 and then tried building it in in vs 2015  I was able to get a successful build once I reinstalled NuGet Package Manager  and closed  then reopened VS 2015   References   Credit There are several SO questions relating to build issues via with earlier version of NPM for VS 2015  i e  I m just passing along what I ve tried and worked out   Recurring resolution is usually update   reinstall NPM or change execution policy in power shell  I tend to like the update   restart approach to avoid tinkering with the black boxes in windows  one source  https   stackoverflow com a 32251092 1158842 There may also be an issue of MSBuild Integrated solutions  in which case migrating away from the NuGet resources in the solution could do the trick  Source  https   stackoverflow com a 31811461 1158842

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Cleaning solution worked for me    I would also advise to close and relaunch Visual Studio once doing so

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You can check the framework on which system was created and developed  and then changes the framework of your current solution to the old framework  You can do this by right click on the solution and then choose properties  In Application section you can change the framework

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Open Project References  I had lots of yellow warning triangles on the various packages  Click Add Reference  just doing that seems to get VS to refresh it references  and the yellow triangles disappeared and the errors from the code also   You might have to do this in a few projects if your solution reference to other projects

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Check the Target framework  changed target framework from  NET framework 4 6 1 to  NET framework 4 6 has worked for me

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For the folks that like me got here because they re trying to host aspnet core mvc in a console application  The ONLY way I was able to solve this was by converting the  csproj to the new format and add the Sdk property to the Project tag on the very first line    lt Project Sdk  Microsoft NET Sdk Razor  gt

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I ve tried all answers above  For me works only removal and adding the reference again described in the following steps   Open  References  under the project  Right click on  System  reference  Click on  Remove   Right click on  References   Click  Add Reference      From right menu choose an  Assemblies   In a search field type  System   Choose  System  from the list  Click  Add  button  IMPORTANT  Restart the Visual Studio

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Try to  Clean Solution Rebuild Solution

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i had to upgrade from visual studio 2017 to 2019  no other proposed solution here helped me  i installed and configured  rebooted every one here plus many other options from ms site   my root cause was probably due to the fact the git repository developer used 2019 and i tried to clone the original git repo into ma 2017

[c#] The type or namespace name 'System' could not be found

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