[SOLVED] Content Pipeline Project: error CS0234 missing assembly

I’m trying to compile a Content Pipeline Extensions
but I get the error CS0234:

CS0234 Namespace ‘Pipeline’ non exists in ‘Microsoft.Xna.Framework.Content’. Missing Assembly. ContentPipelineExtensions C:\DEPOT\FUNHAZARD\WitchProjectMono\ContentPipelineExtensions\ContentProcessor1.cs

I installed MonoGame 3.6 along Visual Studio 2017 Community on Windows 10…

what could it be the problem?

Thank you very much

UPDATE:

I tried to create a Pipeline Extension with Visual Studio 2010 and it has no problems.

Do I have I to switch back to VS2010?

Try repairing VS and reinstalling MG

SOLVED:

I installed Visual Studio 2015 Community Ed