Did your host make any changes to the server recently?

Well, it *sounds* like the Berkeley DB has been upgraded, or that Perl has been compiled to use a different version of Berkeley DB. Which means that your DB files are incompatible with the new version and need to be upgraded, per the instructions in the manual under "I changed hosts..." in troubleshooting.

First, though, you should verify that the permissions on the files in the 'db' directory are 666, and that the permissions on the 'db' directory itself are 777.

All of a sudden the MT login screen rejects my username and password....

I even clicked on the 'forgot your password' link and it then told me after I entered my username that no such author exists!

I can't get into MT! Help! Is there anyway to reset the system and start again with a new login? Or bypass the login screen?

They have made some changes to MySQL....but that shouldn't have affected me. Other than that, no other changes.