NuGet Package Manager: 'AutoMapper' already has a dependency defined for 'Microsoft.CSharp'

The problem is that your NuGet Package Manager is too old. You need NuGet 2.12 since this supports the newer .NETStandard frameworks that the AutoMapper 5.0.1 NuGet package is using.

The AutoMapper has a group dependency which specifies a target framework of .NETStandard. Since your version of NuGet Package Manager is too old it does not recognise this target framework and converts it to an Unknown target framework and you end up with duplicate frameworks since there .NETStandard is used a few times in that NuGet package. This causes the error:

'AutoMapper' already has a dependency defined for 'Microsoft.CSharp'

Unfortunately NuGet 2.12 is not available for Visual Studio 2012 but is available for Visual Studio 2013.

So either you need to update to Visual Studio 2013 or above, or you will have to use the older AutoMapper NuGet package which does not support .NETStandard.

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Seems to be a problem with the current version of automapper:

AutoMapper 5.0.0 Tuesday, June 28, 2016

I tried with the previous version and it works:

PM> Install-Package AutoMapper -Verbose
Install-Package : 'AutoMapper' already has a dependency defined for 'Microsoft.CSharp'.
At line:1 char:16
+ Install-Package <<<<  AutoMapper -Verbose
    + CategoryInfo          : NotSpecified: (:) [Install-Package], InvalidOperationException
    + FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PowerShell.Commands.InstallPackageCommand

PM> Install-Package AutoMapper -Version 4.2.1
Installing 'AutoMapper 4.2.1'.
Successfully installed 'AutoMapper 4.2.1'.

So, if you can't update NuGet Package Manager, the answer is:

PM> Install-Package AutoMapper -Version 4.2.1

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I ended up needing to update NuGet.exe that was included in the solution to be able to build NuGet packages by running:

nuget.exe update -self

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I had the same issue on VS2013. I had to update to VS2013 Update 5 and get the latest nuget distro for VS2013 at https://dist.nuget.org/visualstudio-2013-vsix/v2.12.0/NuGet.Tools.vsix

Once that was done, I rebooted Visual Studio. After that I was able to use the Automapper 5.0.2 package

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Go to Visual Studio > Tools > Extension and Updates

Find Updates in left accordion menu, Go to Visual Studio Gallery.

You will find a update for Nuget.

Update the nuget package and try installing or builing the project.

Thanks, GT

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An other workaround if you're stuck with VS2012 and the old Nuget version:

Find the Cache folder of VS 2012's Nuget Package Manager (with Tools - Options - Nuget Package Manager)

Open AutoMapper.5.x.x.nupkg with your favorite Zip Tool

Modify the file AutoMapper.nuspec - I simply deleted all dependencies except .NETFramework4.5

Add the cache folder as a Nuget source (also in Tools - Options - Nuget Package Manager)

Install Automapper either with the console or the GUI but make sure to choose first the newly added cache folder as package source.

Of course, the next version of Automapper probably needs to be adapted, too, in order to install it.

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This looks like a mismatch between the .NET version used by the Automapper package and your project. Can you confirm the .NET version that your project is using?

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Automapper 6.0.2 - nuget 2.8.8 gives this error. Needed to update to 3.4.4 to get this working.

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Removed both CSharp and AutoMapper. Installed CSharp (4.0.0.0) first and then added Automapper (6.1.1.0). This resolved the problem for me.

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I observed this exact problem when opening a project with Visual Studio 2010.

After opening with VS2017, I was able to install AutoMapper without any error.

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