Traceback (most recent call last):
  File "/usr/lib/gimp/2.0/python/gimpfu.py", line 692, in response
    dialog.res = run_script(params)
  File "/usr/lib/gimp/2.0/python/gimpfu.py", line 353, in run_script
    return apply(function, params)
  File "/usr/lib/gimp/2.0/plug-ins/contactsheet.py", line 189, in Contact_Sheet
    files = images[sheetcount*ThumbsPerSheet:(sheetcount+1)*ThumbsPerSheet]
TypeError: slice indices must be integers or None or have an __index__ method