Develop Reference

"Could not restore packages" in Visual Studio code when opening a project

After each update of MacOS or Visual Studio any project I open throws this error and can't restore packages. It happens in Visual Studio for Mac, the latest version.
Screenshot of the package console
Once I had a similar issue when a vpm connection was active, after disabling it Visual Studio had no issues with packages. But this time I don't have any VPN enabled.

Microsoft suggests the following if restore is not working:
Select the Tools > NuGet Package Manager > Package Manager Settings menu command.
Set both options under Package Restore.
Select OK.
Build your project again.
https://learn.microsoft.com/en-us/nuget/consume-packages/package-restore-troubleshooting
Another suggestion:
Try deleting the project.assets.json file in the obj folder of your project and then right click on the solution and click Restore NuGet Packages again.
https://developercommunity.visualstudio.com/t/restore-nuget-packages-is-not-working/1367227
If those don't work here are other overflow suggestions:
NuGet Package Restore Not Working
Hope this helps!

For those who is interested, I found a solution to this issue.
Execute this command in terminal for the project dotnet nuget locals --clear all
While the project(solution) is opened in the Visual Studio, double-click on the top file (Solution) > Build > General > check the Build with MSBuild on Mono option.

Task could not be loaded from assembly

I have an error in one of my projects at work. The error says:
Severity Code Description Project File Line Suppression State
Error The "StyleCopTask" task could not be loaded from the assembly
C:\Projects\Project
Name\Source\\MSBuild\StyleCop\v4.7\StyleCop.dll. Could not load
file or assembly 'Microsoft.Build.Utilities.v3.5, Version=3.5.0.0,
Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its
dependencies. The system cannot find the file specified. Confirm that
the declaration is correct, that the assembly and all its
dependencies are available, and that the task contains a public class
that implements
Microsoft.Build.Framework.ITask. DskDirectMarketing.Common
Here I can clearly see that there is problem in the relative path which VS is looking for StyleCop. Here is how it looks like:
<Import Project="$(SolutionDir)\MSBuild\StyleCop\v4.7\StyleCop.targets" />
and my SolutionDir declaration looks like this:
<SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\</SolutionDir>
After some digging I noticed that in the error which prompts me there are 2 slashes:
C:\Projects\Project Name\Source\MSBuild\StyleCop\v4.7\StyleCop.dll
First thing I tried was to remove the dash from
<Import Project="$(SolutionDir)MSBuild\StyleCop\v4.7\StyleCop.targets" />
Id didn't worked.
After that I tried to put the absolute path but I had 2 slashes again.
How can I resolve this issue? Any help would be appreciated.

Based on #MaKCbIMKo's answer I installed .Net Framework 3.5 and this fixed my problem.

If you are using Windows 10, enable the .net framework 3.5 and if does not allow you to do so, open command prompt and run:
Dism /online /enable-feature /featurename:NetFX3 /All /Source:D:\sources\sxs /LimitAccess

If you're also using Visual Studio 2019 on Windows 10, you could try the following:
Close your Visual Studio instance.
Open Visual Studio Installer.
On the version of Visual Studio that you're currently using, click on More and select Modify.
Select the Individual components tab.
Search for .NET Framework 3.5 development tools, select it and click on Modify.
Wait for the modification to finish.
Open your project in Visual Studio, then do a Clean, followed by a Build.

In my case the paths were correct, but visual studio needed to run under elevated permissions to access the file in question.

We need to use visual studio installer to install the .netframework 3.5 , if the visual studio installer shows both options Visual Studio 2019 and Visual studio Build Tools 2017. follow below step
If you are using the Visual Studio 2019 ( mine was 16.11.3 but should work for all the versions). you will have Visual studio 2019 and Visual studio build tools 2017 .
Select the Visual Studio Build Tools 2017 => select modify => go to individual components => select .Net Framework 3.5 development tools
Then proceed with the installation.
-Ideally it should work once you re open the Visual studio , if not restart the system

Unity solution not compatible with visual studio

Since updating to the most recent version of Unity 5.4.0f3, whenever I doubleclick on a script, it launches both Visual Studio and Monodevelop, but I get an error saying that the this version of VS (Community 2015) is unable to open my project. Monodevelop displays it's own, somewhat less clear error message. Please see the screen shots below.
I can still manually open my script using Visual Studio's file menu, but the intellisense code completion no longer works. Anyone know how to fix this? I have Visual Studio's Tools for Unity installed.

I was having similar issues when doing a clean download of an existing Unity project onto a fresh install of Visual Studio Community 2019.
In the end the issue for me was that, although the correct version of VS Tools for Unity was installed, it was 'Disabled' by default in VS's Manage Extensions dialog (Extensions -> Manage Extensions). Just had to click 'Enable', restart Visual Studio, and all worked as expected again.

Turns out it was an issue with my existing install of Visual Studio Tools for Unity (VSTU).
I found a thread where users had experienced similar problems due to an unsupported version of VSTU running on Unity5.2 and beyond. Unity 5.2+ requires VSTU 2.1 or later for VS to work correctly with Unity, more information for anyone interested is available in the documentation here.
I had VSTU 2.3 installed, but removing and reinstalling VSTU resolved the issue, so there must have been a problem with my install. If anyone else has this or a similar issue you can download the latest installer for VSTU here. Thanks to all who chimed in your responses helped me look in the right place!

Please try following steps:
Delete old *.csproj and *.sln files on project's root folder
Check "Edit > Preferences > External Tools" and make sure you've selected "Visual Studio"
Re-open solution by "Assets > Open C# Project" menu

For me it was enough to right click the solution in Solution Explorer and run "Resolve errors".

I will complete what is said above. I experienced this issue today and it took me a while. In my case it was relative to a new install of the Unity Editor.
For some unknown reason the unity tool used on VS (intellisense) was uninstalled. I had to reinstall this : open Visual Studio Installer, select your project and reach the Gaming section where reside the tool for Unity.

The extension "Visual Studio 2019 Tools for Unity" seems no longer available for download via the extension manager. Luckily I recalled that I saw some game development features in the Visual Studio installer, so I picked that one:
It works for VS 2019 (16.11.11) and VS 2022 (17.2.0 Preview 1).

Error when building universal app for the store: "Manifest references file 'MyAppName.dll' which is not part of the payload."

I am having this error in Visual Studio 2015 when try to create app package for the store for a windows universal applicaiton:
Manifest references file 'MyAppName.dll' which is not part of the payload.
The error is in the ...\..MyAppSourcePath..\Package.appxmanifest file.
This is somehow related Manifest references file 'Bing.Maps.dll' which is not part of the payload but in my case the error shows up only when build package for the store and is related to the MyAppName.dll (where MyAppName is the name of the name of my application).
Another related question in MSDN: https://social.msdn.microsoft.com/Forums/en-US/f137091e-f550-4eab-b7e2-418149b97d40/error-appx0703-manifest-references-file-myappnamedll-which-is-not-part-of-the-payload?forum=windowsstore

It turns out this is known issue in Windows 10 SDK (Update 1.1). Reference: https://social.msdn.microsoft.com/Forums/en-US/73f2d56d-9e8e-4b57-bcfa-0a972dfd75d7/update-11-generating-store-associated-package-fails-for-a-uwp-application-with-a-winrt-component?forum=Win10SDKToolsIssues
To workaround this issue, add the below ItemGroup in your project file and regenerate the package.
<ItemGroup>
<AppxSystemBinary Include="<Assembly Mentioned in the error>" />
</ItemGroup>
For example, if the assembly name is MyAppName.dll, include:
<ItemGroup>
<AppxSystemBinary Include="MyAppName.dll" />
</ItemGroup>
This ItemGroup can be expanded if the error still occurs for other assemblies, for example:
<ItemGroup>
<AppxSystemBinary Include="MyAppName.dll" />
<AppxSystemBinary Include="OtherAssembly.dll" />
</ItemGroup>

A bug fix for the Visual Studio Tools for Universal Windows Apps (v1.1.1) is released on 5 October 2015. This update requires that you already have the UWP tools v1.1 installed. You can determine whether you have UWP tools 1.1 installed by opening About Microsoft Visual Studio from the Help menu in Visual Studio. If you have “Visual Studio Tools for Universal Windows Apps 14.0.23309.00” installed, then you have the UWP tools 1.1.
To install this update
You must have an internet connection throughout the setup process.
For machines without Visual Studio
Install Visual Studio from https://dev.windows.com/downloads.
For machines with UWP Tools 1.1 installed
Run this installer (http://go.microsoft.com/fwlink/?LinkId=627168) to update the UWP tools to v1.1.1.
For machines without UWP Tools 1.1 installed
For Visual Studio 2015 Community, Professional, and Enterprise, you can install by
Modifying your setup to install the updated tools.
Clicking on the entry for the UWP tools in the Notifications pane.
Using the Extensions and Updates dialog to update Visual Studio.
Running the installer at https://dev.windows.com/downloads, which will add the updated tools to an existing Visual Studio installation.
For Visual Studio 2015 Express for Windows
Run this installer (http://go.microsoft.com/fwlink/?LinkId=624822) to update the UWP tools to v1.1.
To confirm that you have installed the UWP tools 1.1.1 update,
Go to Programs and Features in the Windows Control Panel, and click View installed updates.
Look for “Update for Microsoft Visual Studio 2015 (KB3073097)”, version 14.0.23315
Source: https://social.msdn.microsoft.com/Forums/en-US/73f2d56d-9e8e-4b57-bcfa-0a972dfd75d7/update-11-generating-store-associated-package-fails-for-a-uwp-application-with-a-winrt-component?forum=Win10SDKToolsIssues

I had a hell of a time trying to work this out and it's a slightly different issue to what the OP posted but hopefully this will help someone else out because I couldn't find the answer on StackOverflow and finally found it here: https://social.msdn.microsoft.com/Forums/Sharepoint/en-US/65bc5999-662c-4eda-9967-e1b3031db8c4/error-appx0703-error-manifest-references-file-assetssplashscreenpng-which-is-not-part-of-the?forum=wpdevelop after many hours of mucking around and trying different things.
My error was the same except the file was for the various store and tile image files thus: "Manifest references file 'Assets\Store\StoreLogo.png' which is not part of the payload."
All the files did exist but turned out I was running Visual Studio on a VM using Parallels and the project opened through shared folders and using a UNC path. Ran the project from a mapped drive and it builds all good.
I do realise now that referencing UNC paths using a VM in Parallels Desktop has caused a few issues for me in the past. So just need to keep in mind that things should be run via a mapped drive instead to avoid this.

Error: This template attempted to load component assembly 'Microsoft.VisualStudio.SmartDevice'

I installed Visual studio 2015 and I'm trying to create a test application for Windows Phone 8.1. When I create a new project, I get this message:
Any suggestions on how to solve this problem?

Here is the solution:
Open Visual Studio and go to Tools > Extensions and Updates
Uninstall "NuGet Package Manager for Visual Studio 2015"
Restart Visual Studio 2015
Open Visual Studio and to Tools > Extensions and Updates again
Install "NuGet Package Manager for Visual Studio 2015"
Restart Visual Studio 2015

I got a similar error message when trying to create an MVC Web App on VS2015. Found this solution and it worked for me.
Go to Tools>Extensions and Updates
Search the NuGet Package Manager for Visual Studio 2015
Install NuGet Package Manager
Restart VS2015
Hope it helps.

On VS2017 go to "Tools-> Extension and Updates" then find and Check "Xamarin for Visual Studio", it was disable, i enabled it, and restarted. Worked for me.
Refer:
https://developercommunity.visualstudio.com/content/problem/83460/cannot-create-a-new-xamarin-project-using-vs2017.html

Go to tools>Extensions and updates
Search for Visual studio tools for Apache cordova and enable it.
Restart visual studio and it will work

This worked for me:
1) go to installation path for VS2015 from command prompt and type:
devenv.exe /InstallVSTemplates
2)
- Go to Tools>Extensions and Updates
- Search the NuGet Package Manager for Visual Studio 2015
- Install NuGet Package Manager
- Restart Visual Studio 2015

Another way on VS2017 (and probably VS2019), open the Visual Studio Installer (from the Start menu), and when it loads up, press modify. From there, click on the tab at the top to select individual packages and in the list select NuGet Package Manager. Then press modify at the bottom-right to apply the change.