The message means that you're using a 32bit ODBC driver with a 64bit program. That does not work. If you want to connect with the 64bit DG4ODBC you need to use a 64bit ODBC driver. There's a package available from the Microsoft Technet sites (AccessDatabaseEngine_x64 - http://www.microsoft.com/en-gb/download/details.aspx?id=13255 ) that ships 64bit ODBC drivers for their Excel/Access programs.
Please be aware that installing 32bit gateway products on 64bit Windows is NOT supported.
Thanks - that did the trick, it was also on my "next to try" list of things to do. I'd just assumed that connecting to an old 32bit mdb file I would need to use a 32 bit driver. The 32/64 bit issue is cloudy sometimes, we've had to install oracle 32 bit client on some 64 bit machines in the past to connect to outside sources, so I'd assumed this situation would be similar.