64 bit Gotcha:   If you are creating a DSN on a 64bit machine for a 32 bit database, then you will need to create a 32bit DSN. This cannot be done from the Control Panel  ODBC Data Source Administrator , because this program creates a 64bit DSN. In order to create the 32bit DSN, you must run the program odbcad32.exe from the Windows\syswow64 directory.  The KB article here talks about this issue. In particular, I ran into this problem when moving a VMware Virtual Center from one machine (32 bit, Windows 2003) to a new machine (64 bit, Windows 2008 R2). [more]

http://support.microsoft.com/kb/942976