Do a seach on this forum and you will find a couple other posts realting to your problem.
Here's a basic recap:
The berkelely database that you are using is no longer functioning - becuase of the upgrade. When version of berkeley are upgraded they often change the structure of the database files, thus rendering the files un-readable untill you run an upgrade script.
If you search you'll find an other post where a user has posted the response from support, with MT's sigguested steps as well. Hopefully by following thoes you'll get your site up and working again.
Once things are running, so you self a favor and convert over to MYSQL. You'll avoid these problems, and mt will continue working just fine!