The DTCTester app tests communication to SQL Server via DTC, using ODBC to find your server.  64 bit Windows keeps the DSN’s in two different location – a 64 bit ODBC DSN list, and a different 32 bit list.  So, if you create the DSN in the 64 bit hive, the DTCTester program won’t find it.

To fix, make sure you create the DSN in the 32-bit hive by running %systemroot%\SysWow64\odbcad32.exe.

Posting this for the next time I forget (who uses ODBC anymore anyway!?)…

Tony Rasa Esoterica