smart error leads to app-freeze

[Claude Jones]

With great regularity, SMART locks up on me and produces the following error 
message in a window:
*******************************************************************
Traceback (most recent call last):

  File "/usr/lib/python2.5/site-packages/smart/interfaces/gtk/interactive.py", 
line 180, in callback
    exec code in globals

  File "<callback>", line 1, in <module>

  File "/usr/lib/python2.5/site-packages/smart/interfaces/gtk/interactive.py", 
line 411, in updateChannels
    self._ctrl.reloadChannels(channels, caching=NEVER)

  File "/usr/lib/python2.5/site-packages/smart/control.py", line 354, in 
reloadChannels
    if not channel.fetch(self._fetcher, progress):

  File "/usr/lib/python2.5/site-packages/smart/channels/rpm_md.py", line 73, 
in fetch
    digest = getFileDigest(item.getTargetPath())

  File "/usr/lib/python2.5/site-packages/smart/util/filetools.py", line 31, in 
getFileDigest
    file = open(path)

TypeError: coercing to Unicode: need string or buffer, NoneType found
*****************************************************************
This happens when I've told it to update the channels. Once it happens, the 
update window is frozen as well as the main smart window, and nothing will 
close them including killall smart from a root prompt; the only fix is to 
totally reboot the machine; if I simply log out and then back in again, 
running smart will produce the same error message again - it has to be a 
complete restart...

Ideas?
-- 
Claude Jones
Brunswick, MD, USA