Can't update or install package: An item with the same key has already been added

Question

Problem

In a particular project, I can't update or install any NuGet packages. When I try to do so using the NuGet GUI, it does some work and then stops without saying anything. When I try to do so using the package manager console, I get this output:

PM> Update-Package –reinstall EntityFramework
Attempting to gather dependencies information for multiple packages with respect to project 'SmartCentre', targeting '.NETFramework,Version=v4.5.2'
Update-Package : An item with the same key has already been added.
At line:1 char:15
+ Update-Package <<<<  –reinstall EntityFramework
    + CategoryInfo          : NotSpecified: (:) [Update-Package], Exception
    + FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PackageManagement.PowerShellCmdlets.UpdatePackageCommand

Environment

Visual Studio Professional 2015 Update 1
NuGet 3.3.0.167

What I've tried

Deleting the packages folder
Restarting Visual Studio
Restarting the computer

score 21 · Accepted Answer · answered Jan 17 '16 at 22:54

It turned out that the packages.config file had a couple of duplicates with different versions:

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <!-- ... -->
  <package id="Microsoft.AspNet.Web.Optimization" version="1.0.0" targetFramework="net40" />
  <package id="Microsoft.AspNet.Web.Optimization" version="1.1.2" targetFramework="net40" />
  <!-- ... -->
  <package id="Newtonsoft.Json" version="4.5.11" targetFramework="net40" />
  <package id="Newtonsoft.Json" version="5.0.8" targetFramework="net40" />
  <!-- ... -->
</packages>

Once I removed the duplicates, the problems stopped happening:

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <!-- ... -->
  <package id="Microsoft.AspNet.Web.Optimization" version="1.1.2" targetFramework="net40" />
  <!-- ... -->
  <package id="Newtonsoft.Json" version="5.0.8" targetFramework="net40" />
  <!-- ... -->
</packages>

This solved my problem. Two different versions of a NuGet package in a project I picked up from another developer. Checked what version was actually in use, and then removed the one not in use using Notepad. Reloaded in VS and everything worked fine. Thanks! — John, Apr 19 '16 at 14:57
Thank you so much it has solved my problem too. Very sad to see that Microsoft could not do any better than this while reporting an issue.If it has found out that there is a duplication, i.e. key already exist. Then I don't know why it is so hard for them to tell us which key! Very sad future for them. Long live Open source. — codebased, Apr 10 '17 at 02:04

score 6 · Answer 2 · answered Mar 25 '19 at 13:27

6

If any one is using net core and got this error use command prompt to get detailed error message.

Please run dotnet restore to find the conflicting versions.

Above command need to run form the folder where pjt file resides.

Ex:

 Unable to satisfy conflicting requests for '************': (>= 1.0.1)

 (via package/************ 1.0.22), ************ (>= 1.0.1)

 (via project/************ 1.0.0) Framework: 

 (.NETStandard,Version=v2.0)C:\Users\************\Source\************API.csproj]

answered Mar 25 '19 at 13:27

nandithakw

989
11
16

That helped me find problem. Two different versions of System.Memory referenced by two different packages. – Tedd Hansen May 06 '20 at 12:07
Thank you I almost forgot you could manually dotnet restore and get more details that way. – NIKER Dec 01 '20 at 10:15

Ray · Answer 3 · 2020-08-19T17:56:31.453

The error was a duplicate proj/nuget package. So how do you find the duplicate without removing/re-installing anything?

I ran dotnet restore and got a mountain of error messages. And at the very end got this:

C:\...\NuGet.targets(128,5): 
 error : An item with the same key has already been added.
 Key: (MyLib, 1.0.2) [C:\SomeApp.csproj]

MyLib is the duplicate. Track down all references of it. SomeApp did not reference it directly but indirectly thru another package reference. Seems obvious now but it took me a long time just to read this line. Hope this helps someone.

StefanoM5 · Answer 4 · 2016-08-26T15:19:41.433

2

In my case, i have different packages.config files (one in pcl, one in droid and one in ios), with different package versions. In my packages folder ( Projects\MyProjName\packages ), i have this situations:

I removed only old versions of duplicates and after this i update data in package.config files with right version for example:

 <package id="Newtonsoft.Json" version="8.0.3" targetFramework="net40" />

became

<package id="Newtonsoft.Json" version="9.0.1" targetFramework="net40" />

Now you can re open project and all works fine.

edited Aug 26 '16 at 15:19

answered Aug 26 '16 at 15:13

StefanoM5

1,327
1
24
34

Mine only had the old record and wouldn't allow an update. So following what you did, I just changed the version after DL. Not sure why this happened as I didn't have two. Thank you for the answer it helped! – Mark Rowe Aug 03 '17 at 20:55

score 2 · Answer 5 · answered Dec 03 '18 at 21:01

In my situation, we had a bad nuget.config file checked into our repo. It had settings pointing to two different NuGet repositories that both contained the same packages. We were using NuGet.exe 3.5. Deleting the nuget.config file fixed this issue for us.

Christoph Sonntag · Answer 6 · 2020-03-25T17:30:57.007

This error message is really extremely vague and can mean anything :(

I can recommend this approach for big projects:

Remove all projects from your solution
Readd them one by one until the error appears
Check the .csproj of the project you added last
- Delete big sections from the .csproj
- Try if the error still exists
- Repeat until you can narrow down the section causing the issue (readding the previously deleted sections usually is a good idea)
- Continue until you found something that seems like a duplicate

For me it was the following in my .csproj:

  <RuntimeIdentifier>win</RuntimeIdentifier>
  /* Some more stuff */
  <RuntimeIdentifiers>win;linux</RuntimeIdentifiers>

Removing <RuntimeIdentifier>win</RuntimeIdentifier> solved the problem.

Exactly this is what was causing issue to me – Arpit Agarwal Apr 20 '22 at 22:19 — Arpit Agarwal, Apr 20 '22 at 22:19

score 0 · Answer 7 · edited Nov 22 '17 at 14:58

0

I tried everything and then;

Made sure the Framework was up to date. (for the MVC package I was upgrading)
Uninstalled NuGet and reinstalled it.

It might be worth a try. Doesn't take too long.

edited Nov 22 '17 at 14:58

wonea

4,783
17
86
139

answered Mar 31 '17 at 22:27

pat capozzi

1,412
1
20
16

score 0 · Answer 8 · answered Jul 19 '18 at 08:43

I somehow added two different versions of import references to my csproj file. I had manually edit it to remove the extra reference.

From:

<Import Project="..\packages\Xamarin.Forms.2.5.0.121934\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets" Condition="Exists('..\packages\Xamarin.Forms.2.5.0.121934\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets')" />
<Import Project="..\packages\Xamarin.Forms.3.1.0.583944\build\netstandard2.0\Xamarin.Forms.targets" Condition="Exists('..\packages\Xamarin.Forms.3.1.0.583944\build\netstandard2.0\Xamarin.Forms.targets')" />

To:

<Import Project="..\packages\Xamarin.Forms.3.1.0.583944\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets" Condition="Exists('..\packages\Xamarin.Forms.3.1.0.583944\build\portable-win+net45+wp80+win81+wpa81+MonoAndroid10+Xamarin.iOS10+xamarinmac20\Xamarin.Forms.targets')" />
<Import Project="..\packages\Xamarin.Forms.v\build\netstandard2.0\Xamarin.Forms.targets" Condition="Exists('..\packages\Xamarin.Forms.3.1.0.583944\build\netstandard2.0\Xamarin.Forms.targets')" />

All good.

score 0 · Answer 9 · answered Dec 05 '18 at 12:59

0

The same problem encountered on my side. Uninstall-package followed by Install-package resolved the problem.

answered Dec 05 '18 at 12:59

yi.han

369
4
8

score 0 · Answer 10 · answered Apr 30 '19 at 15:16

In my case, I had packaged multiple assemblies in a custom NuGet package and bumped the version of the primary library, but had forgotten to update the secondary assembly.

My.MainPackage.dll v 1.6 <-- Bumped the version here
My.PackageDependency v 1.5 <-- Forgotten to bump this version

After pushing this bad package, whenever I attempted to Update-Package any project using the previous version, I would get the error

An item with the same key has already been added

Since both the previous and next releases of this package both contained an old version of the secondary assembly.

The solution was simply to rebuild the broken package, bumping both assembly versions again.

FWIW any downstream projects which I had attempted to upgrade with this bad package were left in a half-baked state and needed to be manually edited to get back to a consistent version.

score 0 · Answer 11 · answered Apr 28 '21 at 02:27

0

In my case, even dotnet restore didn't reveal anything. I then did dotnet build .sln using VS command prompt, and it revealed the actual error along with the culprit library and the conflicting versions.

answered Apr 28 '21 at 02:27

stack underflow

197
2
5
18

score 0 · Answer 12 · answered Mar 13 '22 at 18:32

I had this error while validating a new DotnetTool using NuGet Package Explorer, and the reason was that my tool was referencing code from an EXE (instead of DLL) and therefore it was ending up with two different ".deps.json" files. So it's a good idea to avoid referencing EXE files.

Can't update or install package: An item with the same key has already been added

Problem

Environment

What I've tried

12 Answers12

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