title: How to remove add-in (?) from Excel spreadsheet
body: <p>Everytime I open a worksheet, I get this dialog box:</p>
  
  <p><img src="https://i.stack.imgur.com/BY3fI.png" alt="Error message"></p>
  
  <p>I don't really know what it is that is going on here (what is being installed). </p>