Check the userConfig.xml file and see if there is missing data such as empty tags such as the <maxMailboxSize>.  That would point to a corruption.  I've seen many dirty shutdowns where SmarterMail hangs and random userConfig.xml files get corrupted, often missing the passwords and the mailbox size limit.  This would be a different set of circumstances, but it would be helpful if you were able to track down other changes in that file.