file corruption problems and what to do?

["Shankar Gopalakrishnan" <shankargopal@xxxxxxxxxxxxxx>]

Dear all,

I use offlineimap to synchronise between two IMAP email accounts (one
Fastmail and one Gmail) and a local dovecot server that I use with my
mail client.  It was a great success most of the time, and the
occasional offlineimap error was usually remedied just by running it
again.  I use Puppy Linux as my main workhorse system and until recently
was running off a flash drive; however I recently changed it to an
external hard drive, and one of the peculiar problems that this produces
is that when that drive is moved suddenly, it sometimes seems to lose
its connection to the computer.  The result is a system crash - and I'm
guessing from the behaviour of offlineimap, which is the only software
to show significant problems afterwards - file corruption.

After these crashes offlineimap fails repeatedly with AssertionError's,
ValueErrors or "not scriptable" errors, and also starts attempting to
copy messages from the local accounts to the remote accounts (which has
resulted in messages being replicated several times on the remote
server).  Most of these errors appear to happen on one or two particular
folders in the FM account.  The first time this happened, I remedied it
by simply deleting everything (all local folders and the offlineimap
local directory) and running offlineimap as if it was being run for the
first time.  The second time, I restored the two mail local folders and
the offlineimap local directory from a backup, and it seemed to run
fine.  

This time, however, I have the same problem, but restoring the same
backup doesn't seem to have made a difference - the problems are
continuing.  I also tried removing only the local offlineimap folder,
but that has not solved the problem either.  Finally I also tried
removing the main offending folder entirely from the online server, but
that has also not helped.  

Is there any reason that this would be happening?  I can't figure out
why, or what to do.  I can't delete everything again because Fastmail
imposes bandwidth limits on its accounts, and if I do a re-download of
everything again I will run over my limit and have to pay.  Is there any
solution for this?

Thanks very much in advance,

Shankar Gopalakrishnan