title: DotNet Core App 2.1 - Can't add DLL reference
body: <p>I have a DotNetCore 2.1 Web App (just created it today from the VS 2017 scaffold).  This solution also includes a DotNet Core 2.1 Library DLL project.  The solution builds ok.</p>
  
  <p>I have another (brand new) DotNetCore 2.1 Web App that wants to use the Library DLL.  But when I try to add a new reference (on the Browse tab), it complains:</p>
  
  <blockquote>
    <p>One or more errors occurred.<br>
    The reference is invalid or unsupported.</p>
  </blockquote>
  
  <p>Any suggestions?</p>
  
  <p>(Curiously, the DLL doesn't show up directly under the Bin\Debug folder like it does in classic .Net;  It's under Bin\Debug\netcoreapp2.1)</p>