title: .NET Error: The dependency 'Microsoft.Office.Interop.Excel' could not be found
body: <p>My colleague has written a DLL which drives Excel.<br />
  When I reference his DLL in my .NET app, I get a warning:</p>
  <pre><code>The dependency 'Microsoft.Office.Interop.Excel' could not be found. 
  </code></pre>
  <p>My app will compile.<br />
  However, when I get to the bit that uses my colleague's DLL to access Excel, an exception is thrown, with the message above.</p>
  <p>We should have identical setups:  <strong>Windows XP Pro SP3, VS2003, .NET 1.1, Office 2003</strong></p>
  <p>My problem seems similar to <a href="https://stackoverflow.com/questions/224181/net-microsoftofficeinteropexcel-and-interopexcel-dll">this question</a>, but I don't know if it's the same.</p>
  <p>Any help or suggestions gratefully received!</p>
  <h2>Update:</h2>
  <p>Thanks for answers so far!</p>
  <p>I have not added an explicit reference to <code>Microsoft.Office.Interop.Excel</code>.<br />
  Surely I shouldn't have to?<br />
  <strong>However</strong>:  When I tried to add this reference, I cannot find <code>Microsoft.Office.Interop.Excel</code> in the Add Reference dialog.</p>
  <p>Presumably this means that I am missing a DLL?<br />
  ... But I don't understand how that could happen?!</p>
  <h2>Update (fixed):</h2>
  <p>@ConcernedOfTunbridgeWells has the answer that fixed this for me: installing the Primary Interop Assemblies.</p>