For backward compatibility reasons EwE6 uses Microsoft Access for its database system. Not all Windows systems are able to handle Access databases by default; Windows XP and older operating systems provide sporadic support for .mdb files but are not compatible with Access 2007 .accdb files. Windows 7 64-bit versions do not handle 32-bit Access files by default; even having Microsoft Access 2007 or newer installed in 64-bit mode may still render your system unable to handle access to 32-bit Access drivers.
The best way to find out if your system can handle EwE accdb files is by executing EwE. If you are running EwE6, either from a direct installation of from within a development environment such as Visual Basic Express or Visual Studio, and you cannot open EwE models with file extensions that contain the characters 'accdb', then do the follow:
EwE should now be able to load the Access 2007 formatted files.