System could not be found Visual Studio 2017 ASP.NET Core project

Question

I\'ve installed the newly released version of Visual Studio 2017 and started a fresh ASP.NET Core project targeting .NET Core.

Out of the box, I\'m getting the

Answer 1

Try adding the following line above the other references in the csproj file

<Reference Include="netstandard" />

Answer 2

This issue seems to be triggered by a myriad of reasons. Mine was caused by cloning directly from VSTS using Git Bash, my project directory had spaces in it. Git Bash changed those spaces in the path to %20. It was throwing off all the references in my project. So for anyone who tried everything else and are at their wits end, make sure %20 is not in the path.

Answer 3

I had the same problem, first when converting a VS2015 net core mvc web project to 2017 and then when trying to create a new core web application in 2017.

Went to Tools|NuGet Package Manager|Package Manager Settings - checked 'Allow NuGet to download missing packages' and 'Automatically check for missing packages during build in VS' and then clicked 'Clear All NuGet Cache(s)'.

Then re-built the solution - it found and loaded all the required packages and ran OK.

May not work for all cases but simple and worth a try.

Answer 4

I have had the same issue with Visual Studio 2019 and .NET Core SDK 2.2.

These steps solved the problem:

1. Close the Visual Studio
2. Open the Visual Studio as Administrator
3. Open the Solution
4. Right click on Solution -> Restore NuGet Packages

Answer 5

I had this problem too, but not right now, this steps solved my problem: Choose Project -> Properties from the menu bar. In the Project properties window, under Configuration Properties -> General, make sure that Common Language Runtime Support is set to Common Language Runtime Support (/clr)

Answer 6

I also had the same problem. The is no SDK folder under the Dependencies one. Therefore, no Microsoft.NetCore.App libraries !

To solve this problem, in Nuget manager window, install any nuget which depends on .NetCoreApp (you can install for example Microsoft.AspNetCore or BundlerMinifier.Core from the Microsoft Visual Studio Offline Packages source).

The SDK will be restored by the same time.

Once it is back, you can uninstall the previously added nuget. The SDK will remain in place.