script fails to convert cr2 files

[ediKo6]

I'm not able to generate thumbnails for cr2 files.
I always stuck on this error:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 801, in __bootstrap_inner
    self.run()
  File "./synothumb.py", line 56, in run
    self.raw = StringIO(self.dcraw_proc.communicate()[0])
TypeError: initial_value must be unicode or None, not str