crash when trying to scan inaccessible files on mounted camera

I run RPD on Ubuntu 11.04. When I put in a camera and choose RPD, it recognizes the camera but doesn't show any photos.

$ rapid-photo-downloader -d
[INFO/MainProcess] Rapid Photo Downloader 0.4.0
[INFO/MainProcess] Using pyexiv2 0.3.0
[INFO/MainProcess] Using exiv2 0.21.1
[INFO/MainProcess] Using hachoir 1.3.2
[INFO/MainProcess] No downloads have occurred so far today
[INFO/MainProcess] allocating a new mmap of length 4096
[DEBUG/MainProcess] created semlock with handle 3063353344
[DEBUG/MainProcess] created semlock with handle 3063349248
[DEBUG/MainProcess] created semlock with handle 3063345152
[DEBUG/MainProcess] created semlock with handle 3063341056
[DEBUG/MainProcess] created semlock with handle 3063336960
[DEBUG/MainProcess] created semlock with handle 3063332864
[DEBUG/MainProcess] created semlock with handle 3063328768
[DEBUG/MainProcess] created semlock with handle 3063324672
[INFO/GetPreviewImage-1] child process calling self.run()
[DEBUG/MainProcess] Start of day is set to 3:0
[DEBUG/MainProcess] SubfolderFile PID: 20381
[INFO/SubfolderFile-2] child process calling self.run()
[DEBUG/SubfolderFile-2] Finished 0. Getting next task.
[INFO/MainProcess] Detected Canon Digital Camera
[INFO/MainProcess] Detected backup win
[INFO/MainProcess] Detected backup
[INFO/MainProcess] Detected musik
[INFO/MainProcess] Detected win7
[DEBUG/MainProcess] created semlock with handle 3004690432
[DEBUG/MainProcess] created semlock with handle 3004686336
[DEBUG/MainProcess] created semlock with handle 3004682240
[DEBUG/MainProcess] Queue._after_fork()
[DEBUG/MainProcess] created semlock with handle 3004678144
[DEBUG/MainProcess] created semlock with handle 3004674048
[DEBUG/MainProcess] created semlock with handle 3004669952
[DEBUG/MainProcess] created semlock with handle 3004665856
[DEBUG/MainProcess] created semlock with handle 3004661760
[DEBUG/Scan-3] Queue._after_fork()
[INFO/Scan-3] child process calling self.run()
[DEBUG/MainProcess] TaskManager PID: 20383
[INFO/Scan-3] process shutting down
[DEBUG/Scan-3] running all "atexit" finalizers with priority >= 0
[DEBUG/Scan-3] running the remaining "atexit" finalizers
Process Scan-3:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 159, in run
    size = self._gio_scan(source, 0)
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 108, in _gio_scan
    file_size_sum)
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 108, in _gio_scan
    file_size_sum)
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 133, in _gio_scan
    file_id)
  File "/usr/lib/pymodules/python2.7/rapid/rpdfile.py", line 90, in get_rpdfile
    scan_pid, file_id)
  File "/usr/lib/pymodules/python2.7/rapid/rpdfile.py", line 168, in __init__
    self.unique_id = str(scan_pid) + ":" + file_id
TypeError: cannot concatenate 'str' and 'NoneType' objects
[INFO/Scan-3] process exiting with exitcode 1
[DEBUG/MainProcess] created semlock with handle 3004264448
[DEBUG/MainProcess] created semlock with handle 3004260352
[DEBUG/MainProcess] created semlock with handle 3004256256
[DEBUG/MainProcess] Queue._after_fork()
[DEBUG/MainProcess] created semlock with handle 3004252160
[DEBUG/MainProcess] created semlock with handle 3004248064
[DEBUG/MainProcess] created semlock with handle 3004243968
[DEBUG/MainProcess] created semlock with handle 3004239872
[DEBUG/MainProcess] created semlock with handle 3004235776
[DEBUG/MainProcess] TaskManager PID: 20386
[DEBUG/Scan-4] Queue._after_fork()
[DEBUG/Scan-4] Queue._after_fork()
[INFO/Scan-4] child process calling self.run()
[INFO/Scan-4] process shutting down
[DEBUG/Scan-4] running all "atexit" finalizers with priority >= 0
[DEBUG/Scan-4] running the remaining "atexit" finalizers
Process Scan-4:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 159, in run
    size = self._gio_scan(source, 0)
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 108, in _gio_scan
    file_size_sum)
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 108, in _gio_scan
    file_size_sum)
  File "/usr/lib/pymodules/python2.7/rapid/scan.py", line 133, in _gio_scan
    file_id)
  File "/usr/lib/pymodules/python2.7/rapid/rpdfile.py", line 90, in get_rpdfile
    scan_pid, file_id)
  File "/usr/lib/pymodules/python2.7/rapid/rpdfile.py", line 168, in __init__
    self.unique_id = str(scan_pid) + ":" + file_id
TypeError: cannot concatenate 'str' and 'NoneType' objects
[INFO/Scan-4] process exiting with exitcode 1