This was caused by an email without a subject.

An unexpected error occurred during the processing
of your message. The tracker administrator is being
notified.

----  traceback of failure  ----
Traceback (most recent call last):
  File "/usr/lib/python2.2/site-
packages/roundup/mailgw.py", line 287, in 
handle_Message
    return self.handle_message(message)
  File "/usr/lib/python2.2/site-
packages/roundup/mailgw.py", line 457, in 
handle_message
    if subject.strip().lower() == 'help':
AttributeError: 'NoneType' object has no attribute 'strip'