Changing Directory for Failed Request Tracing

I am trying to script the changing of the directory used for the Failed request tracing using the appcmd.exe.  When I run the following:

set FailedRequest="L:\IISLogs\FailedReqLogFiles"

%windir%\system32\inetsrv\appcmd set config -section:system.applicationHost/sites -siteDefaults.traceFailedRequestsLogging.directory:"%FailedRequest%"

The command runs as expected, but when I go into IIS Manager, and check failed request tracing the folder hasn't been changed.  Am I missing something?

Environment: Windows Server 2008 R2 SP1 IIS 7.5

Thanks.

DJ