Are you sure that you have enabled ASP.NET Trace? I don't see this in the config file.
Also, when working with ASP.NET and/or webservices you might want to use "web.nlog" file (located in the same directory where web.config is located). This will prevent your application from restarting when you modify the logging config file. When using *.nlog file make <nlog /> element the root of the document.