what I would do is some time when no one is using the database, go to one of the other workstations that can access the db and create a new blank database. import everything from the existing database into it. then rename or remove the original db and copy this newly created one into it's place. this new db is now unsecured.
then on your workstation (if you are not sure what workgroup you are in), I would go into workgroup administrator and see if you are still joined to the missing mdw file. Just join the standard one in your windows folder.
Hope this helps
Dick