Unable to Install Any Package in Visual Studio 2015

Closing and re-opening VS2015 resolves the issue.

It seems that in some cases, simply reloading the affected project will work.

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tl;dr - Delete this:

%AppData%/Nuget/Nuget.config

Warning: If you had custom NuGet sources, this will remove them, and you'll have to re-add them.

Longer version:

You might have corrupted your NuGet config. Oh no :(

Nuget.config is a file used to keep track of all of the places that NuGet pulls from, as well as configuring other things. More likely than not, this xml file got broken somehow.

Go to this path: C:\Users\{{username}}\AppData\Roaming\

Delete Nuget.config

Restart VS for good measure

For reference: in the good days of 2017, your file should look something like this

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageRestore>
    <add key="enabled" value="True" />
    <add key="automatic" value="True" />
  </packageRestore>
  <activePackageSource>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
  </activePackageSource>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
    <add key="nuget.org" value="https://www.nuget.org/api/v2/" />
    <!-- Others -->
  </packageSources>
  <packageSourceCredentials>
    <!-- secret stuff -->
  </packageSourceCredentials>
</configuration>

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I found a solution for this in my case, try to update the NuGet Package Manager.

To do this:

From VS, go to Tools -> Extensions and Updates Open the Updates menu option at the left, then select Visual Studio Gallery. If there is an update for Nuget Package Installer, it should show in the list to the right. Click Update Restart Visual Studio

This let me install packages without problem again.

Hope this helps!

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In my case updating Microsoft.CodeDom.Providers.DotNetCompilerPlatform and Microsoft.Net.Compilers caused the problem.

Deleting bin, obj, and packages folders and restarting Visual Studio 2015 solved the problem for me.

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In general closing and re-open VS 2015 fixed most problems I have ran across. Once I did need to run a repair on one of my computers.

However I was about to do this Closing and re-opening VS2015 resolved the issue for me I figured that I would instead right click on the project and Unload Project then right click and Reload project THEN Manage Nuget worked!

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You need to Clear All NuGet Caches; for this you need go to Options and click on it like this:

https://i.stack.imgur.com/6dUzy.png

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Just to help out anyone who has landed on this page after updating VS2015 to update 2 and trying to manage packages on a website, receiving the "NuGet configuration file is invalid" error, this is a known and acknowledged issue:

https://connect.microsoft.com/VisualStudio/feedback/details/2698136/nuget-configuration-is-invalid-manage-nuget-packages-for-solution-disabled

I got mine working again by installing package manager 3.4.4 (beta) from http://dist.nuget.org/index.html

They do also state update 3 for Visual Studio will also contain a fix

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My guess is Nuget Package Manager is messing up with VSO. I create a new project, add packages to it just fine, check in TFS. Then I go home, "Get Latest Version", and Run, and fail because Nuget Package Manager doesn't restore my packages. Solution: on my home machine

open Nuget Package Manger, uninstall every packaged that have installed Open References folder, right click > Delete for all the packages you've installed Re-install them via Nuget Package Manager Check in

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I was able to resolve this issue by reinstalling Nuget Package Manager via Tools -> Extensions and Updates

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I had this problem with Visual Studio 2017: It turns out that there are two class library projects - one for .Net and the other for C#. I created the one for .Net and when I tried to install a specific package (Nunit in my case) I got the error message.

Recreating the project as C# class library fixed the problem

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In my case, This problem was caused by a mismatch in my Target framework setting under each project. When I created a new project, VS 2015 defaulted to 4.5.2, however all my nuget packages were built for 4.6.

For some reason, VS 2015 was not showing me these errors. I didn't see them until I created a new empty project and tried to add my nuget project there. This behavior may have been aggravated because I had renamed the project a few times during the initial setup.

I solved the problem by

changing the Target Framework on my projects to 4.6

closed VS 2015

deleted "packages", "obj" and "bin" folders

re-open the solution and try to add the nuget package again.

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I am using Visual Studio 2015 Update 3 and I managed to reproduce this error (despite Update 3 allegedly containing a fix).

As suggested above, a reliable fix is to do the following... 1) Exit Visual Studio, 2) Delete the packages folder, 3) Restart VS.

But... if you don't want to immediately exit VS for some reason, I was still able to add/remove packages from all projects by choosing the 'Manage NuGet Packages for Solution' option, rather than the individual Project with the issue.

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Repairing Visual Studio 2015 seems to have resolved this issue for me. See this issue for NuGet in GitHub.

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Simply restarting Visual Studio works for me.. try restarting Visual Studio.

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I had this problem, which seemed to be caused by something broken in the solution level packages folder. I deleted the contents of the folder and let nuget install all the packages again.

I could then install new packages again.

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Open the packages folder. Check if files with extension .deleteme exists, example Newtonsoft.Json.9.0.1.deleteme. Delete all the packages which have a .deleteme file manually. Delete the .deleteme files. Close and open the Nuget Explorer.

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Change the "package source" in nuget to All

Details: None of the above helped in my case. My problem was that I restricted to only one private feed. Once I changed the "package source" to All, my problem was solved. I believe the crux of the matter is that my private pkg has a dependency on other pkgs from nuget.org.

I hope this can help someone

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In my case, nothing of the above helped. The root cause of the problem in my case was, that I uninstalled the package before and did not check in the change into source control (TFS in my case). After checking in the change (=the deletion of file in the packages folder), I could reinstall the package.

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In my case, there was an empty packages.config file in the soultion directory, after deleting this, update succeeded

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