Based on your error message looks like you are looking for a version that no longer exists and cannot tell which Package source you have selected. I feel like you are looking for version 2.0.0 which is not available in nuget.org repository. The latest one is 2.0.0-rc and it is pre release candidate.
Please try this command if you want to get the latest version
Install-Package -Id Microsoft.Net.Compilers -Version 2.0.0-rc -Source nuget.org
If you want the latest stable version (1.3.2), try this command
Install-Package -Id Microsoft.Net.Compilers -Version 1.3.2 -Source nuget.org
UPDATE
If the package still cannot be installed, then that package may be out of sync between packages.config, packages/ folder and .csproj file
Please follow these steps to perform manual cleanup
- Close visual studio.
- Open .csproj in a notepad or some text editor and manually remove all entries related to Microsoft.Net.Compilers
- Open packages.config in a notepad or some text editor and and remove entry for the Microsoft.Net.Compilers package
- Go to packages/ folder in windows explorer and delete the Microsoft.Net.Compilers folder
- Now start the visual studio and open the solution.
- Now try to install the package again.
Some of the entries that you may have to remove from .csproj as part of step 2 are these
<Import Project="..\packages\Microsoft.Net.Compilers.1.3.2\build\Microsoft.Net.Compilers.props" Condition="Exists('..\packages\Microsoft.Net.Compilers.1.3.2\build\Microsoft.Net.Compilers.props')" />
<NuGetPackageImportStamp></NuGetPackageImportStamp>
<Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
<PropertyGroup>
<ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them. For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
</PropertyGroup>
<Error Condition="!Exists('..\packages\Microsoft.Net.Compilers.1.3.2\build\Microsoft.Net.Compilers.props')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.Net.Compilers.1.3.2\build\Microsoft.Net.Compilers.props'))" />
</Target>