The type or namespace name 'System' could not be found

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:

<ItemGroup>
<Reference Include="Microsoft.CSharp" />
<Reference Include="Sitecore.Kernel, Version=7.0.0.0, Culture=neutral, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\Sitecore.Kernel.dll</HintPath>
</Reference>
<Reference Include="Sitecore.Mvc">
  <HintPath>N:\XXX\Sitecore.Mvc.dll</HintPath>
</Reference>
<Reference Include="System.Web.DynamicData" />
<Reference Include="System.Web.Entity" />
<Reference Include="System.Web.ApplicationServices" />
<Reference Include="System.ComponentModel.DataAnnotations" />
<Reference Include="System" />
<Reference Include="System.Data" />
<Reference Include="System.Core" />
<Reference Include="System.Data.DataSetExtensions" />
<Reference Include="System.Web.Extensions" />
<Reference Include="System.Web.Helpers, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\System.Web.Helpers.dll</HintPath>
</Reference>
<Reference Include="System.Web.Mvc, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\System.Web.Mvc.dll</HintPath>
</Reference>
<Reference Include="System.Web.Providers">
  <HintPath>N:\XXX\System.Web.Providers.dll</HintPath>
</Reference>
<Reference Include="System.Web.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\System.Web.Razor.dll</HintPath>
</Reference>
<Reference Include="System.Web.WebPages, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\System.Web.WebPages.dll</HintPath>
</Reference>
<Reference Include="System.Web.WebPages.Deployment, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\System.Web.WebPages.Deployment.dll</HintPath>
</Reference>
<Reference Include="System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  <SpecificVersion>False</SpecificVersion>
  <HintPath>N:\XXX\System.Web.WebPages.Razor.dll</HintPath>
</Reference>
<Reference Include="System.Xml.Linq" />
<Reference Include="System.Drawing" />
<Reference Include="System.Web" />
<Reference Include="System.Xml" />
<Reference Include="System.Configuration" />
<Reference Include="System.Web.Services" />
<Reference Include="System.EnterpriseServices" />

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.

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.

Cleaning solution worked for me.

I would also advise to close and relaunch Visual Studio once doing so.

Follow these steps :

1. right click on Solution > Restore NuGet packages
2. right click on Solution > Clean Solution
3. right click on Solution > Build Solution
4. Close Visual Studio and re-open.
5. Rebuild solution. If these steps don't initially resolve your issue try repeating the steps a second time.

Thats All.

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