title: upgrade asp.net core targeting framework 4.6.1 from vs2015 to vs2017 - One or more compilation references are missing
body: <p>I have upgraded my asp.net core,using project.json and targeting .net framework 4.6.1 on visual studio 2015 to visual studio 2017.</p>
  
  <p>I have multiple projects in the solution where the main application is referencing them by project reference(all of them target net461).</p>
  
  <p>When running the application I get </p>
  
  <blockquote>
    <p>One or more compilation references are missing. Possible causes
    include a missing 'preserveCompilationContext' property under
    'buildOptions' in the application's project.json.</p>
  </blockquote>
  
  <p>screenshot:
  <a href="https://i.stack.imgur.com/JDvpM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JDvpM.png" alt="enter image description here"></a></p>
  
  <p>I have tried adding the     true
  to all of the reference projects without luck.</p>
  
  <p>Can anyone help? Thank you.</p>