If you get a pop-up message with a System.InvalidOperationException on starting Duplicate Cleaner (or TextCrawler) you may have a damaged font file on your computer.  Check to see if the message mentions a font type - e.g. Arial.

To repair the font (assuming font type of Arial):

  • From the start menu find the 'Run' command, or type 'run' into the search box.
  • Enter the filename c:\windows\fonts\arial.ttf (assuming your system drive is c:)
  • Click install on the window that appears to re-install the font.
Try starting the program again to see if the issue is fixed.