I have enabled the ODBC trace file on windows and I can see that the ODBC trace file is being created, but it is empty.
I'm using the Data Direct Drivers, but nothing is written to the ODBC trace file.
On windows systems the ODBC layer is part of the operating system.
This issue has been documented by Data Direct and Microsoft as well:
http://knowledgebase.datadirect.com search for "ODBC Tracing on Windows Creates No File or Empty File"
If the Policy Server is running as a service, therefore you may need to enable the option "Machine-Wide tracing for all user identities" under the "Tracing Tab".