The DefaultHttpHandler.OverrideExecuteUrlPath method returns null unless it is overridden in a class that is derived from the System.Web.DefaultHttpHandler class.

The DefaultHttpHandler.OverrideExecuteUrlPath method is called only if ASP.NET is running in worker process isolation mode on IIS 6.0, and if the response was not modified before the System.Web.DefaultHttpHandler object was called. The response is modified by any of the following:

• Calling erload:System.Web.HttpResponse.Write.

• Calling HttpResponse.AddHeader(string, string).

• Calling HttpResponse.Flush.

• Changing the cache policy for the response.

• Adding a System.IO.Stream object as a filter to the HttpResponse.Filter property.