On an 64-bit operating system (Itanium or x64), Windows installs two versions of the "Data Sources (ODBC)" service: a 32-bit version and a 64-bit version.  A 32-bit native (non-CLR) data application that will run under WOW64 needs to use a data source that was created with the 32-bit "Data Sources (ODBC)" service.

If you will build and run an application as a 32-bit application on a 64-bit operating system, you must create the ODBC data source with the ODBC Administrator in %windir%\SysWOW64\odbcad32.exe.

David Schwartz
SQL Server User Education