Your project is not referencing the “.NETFramework,Version=v4.5” framework.

I actually just figured out the problem. I ended up clicking on Restore Nuget Packages at the solution level and I managed to compile my PCL file, and then the rest of my solution.

Hope this helps.

I had this same problem, and I ended up having to not only delete the contents of bin and obj folders, but also the .vs directory for the solution.

crimbo

I had the same problem - this occurs still using Visual Studio 2017.3, which uses .csproj files instead of project.json. Interestingly, the error message still contains the text "project.json".

It appears the cause of this issue is a lock file or obj\project.assets.json file (depending on your version of VS) from a previous build, which is not removed during a clean, as described here.

Manually deleting the /obj directory is a quick workaround.

If you have a "new" project (eg .NET Core or netstandard project created in VS 2017) and an "old" project in the same directory (eg .NET 4.6 project created in VS 2015), it appears they will continually fight because they both use the ./obj dir in different ways. More info here..

The msbuild workaround is to make one of your projects use a different obj dir. I added this to my "old" csproj:

<PropertyGroup>
  <!-- Needed due to old project and new project in same directory: https://github.com/NuGet/Home/issues/5126 -->
  <BaseIntermediateOutputPath>obj_netfx\</BaseIntermediateOutputPath>
</PropertyGroup>

I found that a rogue project.lock.json was causing this issue for me. Once I deleted the file, the problem went away.

Here is some documentation on project.lock.json.

Some further advice would be to ensure that project.lock.json is ignored in your git ignore file, and to try a full git clean. Make sure you understand the implications of a Git clean before you do that though.

I had the same issue after updating to Visual Studio for Mac 7.4 (build 1033):

Error: Your project is not referencing the "MonoAndroid,Version=v7.1" framework. Add a reference to "MonoAndroid,Version=v7.1" in the "frameworks" section of your project.json, and then re-run NuGet restore.

I don't have any json project files. The tips in here did not help either, so I had to find out the hard way that I had to install the lastest Android SDK (Oreo 8.1) in addition to my target SDK (Nougat 7.1).

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ch sandeep kumar

I have same issue, but i've solved by adding proper nugget package resource at vs2017-->tools-->options-->Nugetpacakge manager--->updated the proper package url.

Refer below image

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I am having the same issue but in a different way.

        Your project does not reference ".NETFramework,Version=v4.5" framework. Add a reference to ".NETFramework,Version=v4.5" in the "TargetFrameworks" property of your project file and then re-run NuGet restore.          

Added reference in TargetFrameworks property.

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Rebuilt the project after deleting obj bin and .vs. Still it throws the same.