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:

<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.

Solution 1

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

Solution 2

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.

Solution 3

Cleaning solution worked for me.

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

Solution 4

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.

Solution 5

Unload project -> Reload project normally fixes this weird, Nuget related, error to me.

View more solutions

Comments

[hubson bropa]

nothing odd there. do you have a using clause for it n your views? if not you may not have to, i bet you can add it implicitly via the Views web.config...see this question stackoverflow.com/questions/12547641/…

[Hélder Gonçalves]

the issue is not only with the using clauses.. it's also when I try do to @Html, please see the updated question

[Backs]

what VS version do you use? what MVC version of your project?

[hubson bropa]

did you have this project in a previous version of visual studio? if so it may be a nuget package restore issue....stackoverflow.com/questions/27895504/…

[Hélder Gonçalves]

@hubsonbropa When I open the project in VS 2013 it works fine. This only happens in VS 2015

[RBT]

Related post - Getting "type or namespace name could not be found" but everything seems ok?

[StuartLC]

Yet another reason why VS can't find any of the System is because it can't install a framework or core dependency dll is because the nuget package sources have been deleted or corrupted. Make sure that at least https://api.nuget.org/v3/index.json is added

[monty]

This worked for one of my solutions that had this problem; but another required VS to be relaunched after cleaning.

[WasiF]

clean solution, restart visual studio and build solution... this worked, Thanks

[pollaris]

You need to leave your XAML and CS windows open when you close VS.

[CularBytes]

Hahaha when you spent half an hour trying to install .NET standard while it seems you already have everything. Thanks

[Andrew]

How do you "clean" the solution? Right click > Clean

[Nil]

Solution Explorer -> Right click on your project -> Clean

[rsmith]

The issue for me seemed to be that the framework was already downgraded (4.5) compared to my other projects (4.5.1). Upgrading the framework to 4.5.1 & closing VS, re-opening & then building worked. Upvoted since this was the only one that mentioned the framework. Thanks!

[RayLoveless]

I needed to run step 4 before step 3.

[kcho0]

Agree, just restarted VS (A.K.A. "IT Weapon of Choice") worked for me too.

[SendETHToThisAddress]

It probably resolved your issue because VS 2019 has more built-in mechanisms for automatically resolving issues.

[SendETHToThisAddress]

I recommend adding this to your post: "5. Rebuild solution. If these steps don't initially resolve your issue try repeating the steps a second time."

[Marcelo Luz]

For me, restarting Visual Studio (after rebuilding the solution) solved the problem.

[0xcrypto]

Instead of cleaning the solution, you should rebuild the solution. Clean only if rebuilding the solution didn't work.

[Roro]

Cleaning and rebuilding worked for me.

[Suncat2000]

I second this post. Sometimes cleaning the solution is not enough and rebuilding the solution will repair the references.