I work for a call center and the same thing is happening to us, very frequently. When we get the tone, the customer is usually still on the line. When we close out X-lite the tone continues. If you CTL-ALT-Delete and go into task manager, you can see the x-lite process still running, if you end the process you can log back into x-lite without having to reboot your computer. We are still investigating what the hect is causing this problem. We used wireshark to capture packages and are in the process of analyzing those right now. I will keep you posted on anything I find.