We (collectively, not royally :-) ) had this problem on our system
some time back. Turns out there was a message with a ' in the
Subject line, and when MHonArc stored that ' in its dbfile it
mistakenly read it as a string terminator for the value in the
hashtable. As I recall, the solution was to edit the mail file
and escape the offending apostrophe before rebuilding the archive.
This problem should not exist in 2.0b3. The quote problem was fixed
awhile back. The only way it should be a problem now is if the
.mhonarc.db was created by an old version of mhonarc and then 2.0b3
was used later to process it.