title: Web app doesn't deploy: Sorry, unable to open the file at present
body: <p>I have a AppsScript in my Google Sheet that I want to deploy as a WebApp (something I've done many times before).
  I have deployed it as public (Anyone, even anonymous), and the link comes up with:
  "Sorry, unable to open the file at present.
  Please check the address and try again."</p>
  
  <p>This also happens when I click "Test web app for your latest code"</p>
  
  <p>The script works perfectly from within the spreadsheet, and my deployment code is:</p>
  
  <pre><code>    function doGet() {
    return HtmlService.createTemplateFromFile('Weekly.html')
        .evaluate();
  }
  
  function onOpen() {
    var Menu = SpreadsheetApp.getUi() // Or DocumentApp or FormApp.
        .createMenu('Survey');
        Menu.addItem('Run Survey', 'doSurvey')
          .addToUi();
  }
  
  function doSurvey() {
    var html = HtmlService.createTemplateFromFile('Weekly.html')
        .evaluate();
    SpreadsheetApp.getUi() // Or DocumentApp or FormApp.
        .showModalDialog(html, ' ');
  }
  </code></pre>
  
  <p>Any hints?
  Thank you!</p>