Log file names now support the use of environment variables. You can include environment variables such as %WINDIR%, %TEMP%, and %USERPROFILE% in the Filename property of the Flat File Trace Listener, Rolling Flat File Trace Listener, and XML Trace Listener.

<add name="Trace" type="Microsoft.Practices.EnterpriseLibrary.Logging.TraceListeners.FlatFileTraceListener, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
listenerDataType="Microsoft.Practices.EnterpriseLibrary.Logging.Configuration.FlatFileTraceListenerData, Microsoft.Practices.EnterpriseLibrary.Logging, Version=5.0.414.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"
fileName="Logs\trace_%DATE%.log" header="" footer="" formatter="Trace"
traceOutputOptions="None" filter="All" />

Имя файлав итоге - trace_.log, что я делаю не так?