Sometimes called FREB, the request-based tracing provides a good way to figure out what exactly is happening with your requests and why, provided you can reproduce the problem you are experiencing. Problems like poor performance on some requests, or authentication related failures on other requests, or even the server 500 error from ASP or ASP.net can often be very difficult to troubleshoot--unless you have captured the trace of the problem when it occurs.

The following video shows how to configure trace on any IIS7 site once the feature has been enabled.
http://channel9.msdn.com/posts/dunnry/Failed-Request-Tracing-on-IIS7/

More details on Tracing may be found here.
http://www.iis.net/ConfigReference/system.webServer/tracing

Please note that remote administration must be enabled in order to perform a trace on your site via the IIS Management Console [more].

*Although this is a delegated feature, it still requires for one of our systems administrators to enable the feature on the server side.

**Should you see an alert on the top right corner of the IIS manager that displays "Failed Request Tracing is not enabled for this Web Site..." you must contact support@appliedi.net your site name and request that we enable FREB or Failed Request Tracing as this message means FREB is not enabled.

***All trace files will bewritten to your domainslogs trace folder by default although this path may be changed at your request. For security reasons we recommend you do not write logs to any directory below WWWROOT.