错误处理Your project does not reference ".NETFramework,Version=v4.0" framework. Add a reference to ".NETFramework,Version=v4.0" in the "TargetFrameworks" property of your project file and then re-run NuGet restore.

错误信息：

Your project does not reference ".NETFramework,Version=v4.0" framework. Add a reference to ".NETFramework,Version=v4.0" in the "TargetFrameworks" property of your project file and then re-run NuGet restore.

解决方案一： 不要同时打开两个具有共享项目文件夹的解决方案，并且注意切换的时候删除 obj 和 bin 文件夹。

解决方案二：添加以下代码到 .NET Framework 的项目文件（.csproj）中：

<Project>
  ...  <PropertyGroup>
    <BaseOutputPath>$(MSBuildProjectDirectory)/out/$(MSBuildProjectName)/bin</BaseOutputPath>
    <BaseIntermediateOutputPath>$(MSBuildProjectDirectory)/out/$(MSBuildProjectName)/obj</BaseIntermediateOutputPath>
  </PropertyGroup>
  ...</Project>