Behavior:
A 64-Bit DSN cannot be selected in ACTIVE IMPORT.
Solution:
If you set up a new user/system DSN for index enhancement with ACTIVE IMPORT, you must take note of the following for 64-bit operating systems:
If you create a new DSN via Control Panel >Administrative Tools > Data Sources (ODBC), it will be a 64-bit DSN. These cannot be selected in ACTIVE IMPORT.
To set up a 32-bit DSN in a 64-bit operating system, use the odbcad32.exe program, located in %systemdrive%\Windows\SysWoW64. A DSN created in this way can be selected in ACTIVE IMPORT.
Please refer to: http://support.microsoft.com/kb/942976