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
The type or namespace name 'System' could not be found (are you
missing a using directive or an assembly reference?)
error. Any idea what's causing this and how to fix it?
Also, looks like there are problems with NuGet packages as well:
I also tried dotnet restore on the project through the command line and got the following error:
P.S. Kind of disheartening that you get an error in a fresh new project in the latest version of Visual Studio 2017!
UPDATE:
SDK version is v 1.0.1 -- see below:
UPDATE 2:
This is very strange. Looks like the original problem was due to NuGet package source pointing to a folder under Visual Studio 2015 folder. I unchecked it and left only nuget.org. With that my project seemed to have restored all the packages and when I started the project it loads up the standard ASP.NET page. But if I open startup.cs file, I get red squigglies all over the place but if I run the project, it works fine. What's going on here?
UPDATE 3:
I closed the project and VS 2017. I then restarted VS 2017 and opened the project and now it seems to be fine. And I'm not referencing the .NETStandard library 1.6.1 and everything seems to be working fine now.
I had the same issue in my Visual studio 2017 .Net Core application. I closed the Visual studio and re-open fixed everything.
Came across the same issue today. I had an old nuget source that no longer existed. So I went into Tools > Nuget Packet Manager and un-checked the wrong one. Hit "Ok", and then rebuilt the project, and it works great now. It seems like you stumbled onto it, but also wanted to verify that it fixed my issue, and it does.
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.
Multiple closing and reopening of VS2017 fixed it for me.
I had the same issue, the solution for me was to clear the NuGet cache. Tools > NuGet Package Manager > Package Manager Settings > Clear All NuGet Cache(s)
Check the version .NET Command Line Tools in CMD, just type dotnet --info. If version is 1.0.0, then try to install latest version .NET Core SDK from here.
Find the broken project and right click, Unload, right click, Re-load. Fastest fix for me.
If you get the problem while using the CLI, try doing nuget restore instead of dotnet restore as that sometimes pulls down packages that the dotnet CLI seems to miss.
I have had the same issue with Visual Studio 2019 and .NET Core SDK 2.2.
These steps solved the problem:
Close the Visual Studio
Open the Visual Studio as Administrator
Open the Solution
Right click on Solution -> Restore NuGet Packages
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.
'System' reference you can replace with any you need.
Try adding the following line above the other references in the csproj file
<Reference Include="netstandard" />
For me the problem was caused by my project having a custom IntermediateOutputPath. For some reason, if project_name.csproj.nuget.g.targets is not in obj subfolder of project folder, the error occurs.
Using default IntermediateOutputPath or keeping a shadow copy of project_name.csproj.nuget.g.targets in fake obj folder solves the problem for me.
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.
So, I have cloned the repository from github and started getting this error.
It was my project uploaded from another machine. I later realized that I have used the materialdesign packages in my project.
I have uninstalled and reinstalled these packages and it fixed my issue.
Had the same problem. Uninstalled Application Insights from my projects using the nuget package manager. I'm not looking at that yet, I just wanted core and unit tests. Problem solved.
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.
Not quite sure in which order vs 2017 trying to resolve packages.
But my situation was following. In my VS2015 I had configured local and 3rd party source for nuget packages, newly installed version of 2017 loaded them too.
https://api.nuget.org/v3/index.json was first in list.
But vs2017 throwed an error that it can't restore .net core libraries from my another local repo.
After I unchecked all of them except https://api.nuget.org/v3/index.json, it had started to working normally.
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)
Simply opening the NuGet package manager and then the Visual Studio settings related to it - without changing anything - merely looking around, and when I closed out, the problem was gone.
This seems to be an intermittent issue that can come and go for no obvious reason.
None of the answers here worked for me so I'm posting what did work.
My errors were mostly the same as the original poster but I also had:
Error loading meta data for 'Microsoft.Extensions.FileProviders.Embedded.2.0.1'
hexadecimal value 0x1C invalid character
Every time I attempted to download a different nuget package or restore old packages I would see this error. I also saw the other errors such as:
type or namespace system could not be found
What worked for me:
opened the filepath that the error said the bad metadata was in, which for me was C:\Program Files\dotnet\sdk\NuGetFallbackFolder\microsoft.extensions.fileproviders.embedded\2.0.1
Then, I put the contents of that folder into another folder I named "hiding".
Then, I went back to the nuget package manager and tried to install a package, hoping to have the SDK restored. IOt worked successfully, and all my other errors were gone as well, and the fresh new project runs as it should!
The problem for me occurred when running my Visual Studio as Admin with a separate user-- I had created a Git Repo with the source files in the user documents of my normal account. When I created a new solution in that folder the above errors occurred. Try creating your project in a different place and see if the error still occurs.
I was facing the same issue when I created a new project (.net Core 2.2) in VS2019.In my case there was an Azure package which was creating the problem.I uninstalled it and the project started working fine.
Run mentioned below command to uninstall the package.
Uninstall-Package Microsoft.VisualStudio.Azure.Containers.Tools.Targets -Version 1.7.10
I had the same problem. I cloned a github project and this error came. So I deleted the cloned project and then I cloned the project again and it worked fine.
I try to analyze my .net solution with HP FORTIFY from visual studio .But I am unable my web project and got pre compilation error message . I tried to trouble shoot from command prompt and got "could not load file or assembly Oracle.Dataacess ".
In my solution one of the project refers Oracle.Dataacess dll and that project is refered by the web project .I tried to use x64 version of the dll . But I still got the error .
Appreciate your suggestions to get rid of this pre compilation error .
Thanks,
Bala
My preferred method of debugging precompiler issues is to add this command into the post-build event of the web project in Visual Studio, that way the error shows up in the error list.
"C:\Windows\Microsoft.NET\Framework64\v4.0.30319\aspnet_compiler.exe" -v / -p $(ProjectDir)
Another thing to keep in mind, if you have files that are not part of the solution but are part in the web projects directory, the aspnet_compiler will still read them.
I find this situation common when developers would excluded files from Visual Studio. This does not delete them. Or if they delete them, then delete through the Visual Studio interface but not from the underlying source code repository and they just get downloaded again on checkout.
An easy way to check this would be to turn on Show All Files in the Visual Studio Solution Explorer window.
Hello i am currently learning ASP.NET MV4 with Visual Studio 2012, i created a new project, not an empty project, an internet application but anytime i try to run it i keep getting an error.
There is no much else i can say about this, i am just now learning ASP.NET with Razor.
I would very much appreciate some help on this. The error itself seems to be originating from my machine.config file but i'm kinda afraid of opening that file.
This is the error:
http://prntscr.com/3a6ltl
Add MySQL.Web as your reference with NuGet Install-Package MySql.Web.
Or remove the red line from your machine.config if you are not going to use the MySQL Membership provider
It is located here: c:\windows\microsoft.net\framework\v4.0.30319\config\machine.config
I just added an existing MVC project to VS 2012 that i downloaded from Codeplex. The problem is when i'm trying to build or run the project i get a lot of errors that VS can not find references and namespaces. If i open a new MVC project then i'm not getting this errors and everything runs fine. So it only occurs when i try to open an existing project.
Can someone help me with this please?
From the VS 2012 menu select Tools->Library Package Manager->Package Manager Settings. A window will appear. Check the checkbox labeled "Allow NuGet to download missing packages during build" under the Package Manager->General heading. Click the OK button to apply the setting.
Next in the Solution Explorer right-click the Solution node and select Enable NuGet Package Restore. Perform a Clean Solution and then a Build Solution. A .nuget folder should be downloaded into your solution and all compile errors related to missing references should be resolved.
This is what worked for me.
I'm trying to install some custom made project templates for asp.net MVC4, however my Visual Studio 2012 Premium won't show the new templates. The templates are installed by a .VISX file like this one: http://www.asp.net/single-page-application/overview/templates/hottowel-template
Visual Studio is showing this file as an "Enabled" and "Installed" Extension, but when I try to create a new ASP.NET MVC4 project it is not showing those templates as an option like shown in this image:
I'm just seeing the regular options and it is not showing me the Hot-Towel template or any other single page application template. Could you please tell me how to fix this if one of you guys knows.
I fixed this by installing ASP.Net Web Tools Update Pack Fall 2012:
http://www.asp.net/vnext
I decided to give the answer to my own question for helping others with the same question.