[Spambayes] Spambayes log file shows failure and spam not being caught.

[Mark]

The following is a bit of my procmail log file showing an issue with 
spambayes.
I've not seen the filter reliably catch anything, in spite of training 
on several hundred messages. 
Any ideas?

Traceback (most recent call last):
  File "/usr/bin/sb_filter.py", line 283, in <module>
    main()
  File "/usr/bin/sb_filter.py", line 274, in main
    action(msg)
  File "/usr/bin/sb_filter.py", line 192, in filter
    return self.h.filter(msg)
  File "/usr/lib/python2.6/site-packages/spambayes/hammie.py", line 156, 
in filter
    debug, train)
  File "/usr/lib/python2.6/site-packages/spambayes/hammie.py", line 110, 
in score_and_filter
    prob, clues = self._scoremsg(msg, True)
  File "/usr/lib/python2.6/site-packages/spambayes/hammie.py", line 39, 
in _scoremsg
    return self.bayes.spamprob(tokenize(msg), evidence)
  File "/usr/lib/python2.6/site-packages/spambayes/classifier.py", line 
196, in chi2_spamprob
    clues = self._getclues(wordstream)
  File "/usr/lib/python2.6/site-packages/spambayes/classifier.py", line 
499, in _getclues
    tup = self._worddistanceget(word)
  File "/usr/lib/python2.6/site-packages/spambayes/classifier.py", line 
514, in _worddistanceget
    prob = self.probability(record)
  File "/usr/lib/python2.6/site-packages/spambayes/classifier.py", line 
317, in probability
    assert spamcount <= nspam, "Token seen in more spam than spam trained."
AssertionError: Token seen in more spam than spam trained.
procmail: Program failure (1) of "/usr/bin/sb_filter.py"
procmail: Rescue of unfiltered data succeeded
 From mark  Sun Dec 13 19:27:22 2009
 Subject: For fairlane special 80% OFF on Pfizer
  Folder: 
/home/mark/Maildir/new/1260750442.15020_2.cyclops                2158