I fixed a problem in a try and error way, I don't understand what I did and need explanation!!
When connecting to WCF service I got exception with message
The HTTP request was forbidden with client authentication scheme 'Anonymous'.
After a lot of trials related to IIS 6 configuration, I notice that the only application on the Default App pool is that WCF web service, I created App pool and assigned it to the service, it works!! Why??!!!