No solution yet, just some more leads. I won't be able to try them out for several hours, so you might get to them before I do.

Microsoft Support Online offers some articles that might help:

Q98743: Err: Not a Database File - different error message but possibly the same cause.
Q139758: How to Modify the Table Header

Also mentioned there was another 3rd party tool, Recover, available at http://abri.com/recover.html. ($70 single-user).