This is typically a transient error that resolves itself by refreshing the browser.  Several refreshes may be needed in order for the PC to fully download the setup.exe file and progress through the installation.  Here are the steps that we've found resolve the issue the fastest:
  1. Delete the temporary internet files from Internet Explorer (Tool > Internet Options > Delete)
  2. Close all open browser windows
  3. Open a fresh browser window
  4. If the error appears when browsing to the GUAPPLE, press Crtl+F5 to force the page to reload
  5. If using Crtl+F5 doesn't resolve the error after two or three attempts, repeat these steps starting at #1