title: ADD-IN ERROR This add-in could not be started
body: <p>Using the Visual Studio 2017 C# Excel 2016/2019 Web Add-In template, I'm trying to create a Basic Add-in to "Insert content into Excel spreadsheets [VS option for project]."</p>
  
  <p>All my attempts fail in Excel when I run the project with the message: 'ADD-IN ERROR This add-in could not be started. Close this dialog to ignore the problem or click "Restart" to try again.' Clicking Restart displays a "Loading" dialog in Excel that never completes.</p>
  
  <p>I've unsuccessfully tried all the following steps to resolve this problem:</p>
  
  <ul>
  <li>Run VS in admin mode </li>
  <li>Switched from Excel 2016 to 2019</li>
  <li>Reset IE settings (ensuring protected mode is on for Internet and Restricted sites)</li>
  <li>Upgraded to Windows Build 1809</li>
  <li>Reset the Excel add-in cache</li>
  </ul>
  
  <p>In addition, I ensured that the localhost SSL certificate is trusted and I can browse to the IIS Express site with no security warnings.</p>
  
  <p>I should note that this issue is happening only with VS2017 templates. If I use node and sideload the add-in, I have no issues on this particular dev machine.</p>
  
  <p>My question is:</p>
  
  <ul>
  <li>How do I go about getting more information from Excel or VS2017 on why the add-in is not loading and this error?</li>
  </ul>