title: Testing my NuGet package, "project cannot be viewed in the object browser" error with package but not with the comprising DLL
body: <p>I am making a NuGet package which targets .Net Standard 1.3 and .Net Fx 4.5.</p>
  
  <p>To do this, I have a solution with my NetStandard version of the code, which is highly tested, and I copy across the two *.cs files to a duplicate project which targets Fx 4.5 - I didn't know a better way to do it. This is my first time targeting multiple frameworks.</p>
  
  <p><a href="https://i.stack.imgur.com/W2blQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/W2blQ.png" alt="Solution structure"></a></p>
  
  <p>I then have a <code>nuspec</code> file which looks like this (metadata has been snipped for brevity):</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;package&gt;
    &lt;metadata&gt;
      &lt;snip/&gt;
    &lt;/metadata&gt;
    &lt;files&gt;
      &lt;file src="VillageSoftware.PathMatcher-NetFx45\bin\Release\VillageSoftware.PathMatcher-NetFx45.dll" target="lib\net45\VillageSoftware.PathMatcher.dll" /&gt;
      &lt;file src="VillageSoftware.PathMatcher\bin\Release\netstandard1.3\VillageSoftware.PathMatcher.dll" target="lib\netstandard1.3\VillageSoftware.PathMatcher.dll" /&gt;
    &lt;/files&gt;
  &lt;/package&gt;
  </code></pre>
  
  <p>I can successfully pack this with <code>nuget pack VillageSoftware.PathMatcher.nuspec</code></p>
  
  <p>I was initially testing the package using a local (<code>C:\</code>) package source but have since pushed the package to NuGet.org</p>
  
  <p>To test, I created a new .Net Framework 4.5 Console App, and when I install my package using either <code>Install-Package</code> or the 'Manage NuGet Packages' window, the reference shows up with an exclamation on it:</p>
  
  <p><a href="https://i.stack.imgur.com/jlNkT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/jlNkT.png" alt="Package with error icon"></a></p>
  
  <p>Double clicking the reference throws up an error message box:</p>
  
  <blockquote>
    <p>This project cannot be viewed in the object browser because it is unavailable or not yet built. Please ensure that the project is available and built.</p>
  </blockquote>
  
  <p>Contrastingly, if I use 'Add Reference' to add the VillageSoftware.PathMatcher DLL directly to the TestBed project, it works fine.</p>
  
  <p>My theory is that the frameworks between the package and the host project are not matching up, but I don't know why! The package packs up fine, and the successful Install-Package shows that NuGet is using the correct lib, not the NetStandard version. I don't think my lib has any dependencies which I've missed in the nuspec.</p>
  
  <p>Why is this happening?</p>