In some circumstances, the 'oldvalues' argument to
generateChangeNote (roundupdb.py, line 578) is a
string, not a dictionary.  

I've seen this with mailgw and ZRoundup.  At least in
the case of mailgw, the string is the message trailer
(property list).

A temporary workaround is to catch the AttributeError
exception and return an "error" string instead.