Did you read the documentation at
http://wiki.flightgear.org/index.php/FGCom_3.0 ?
If the echo test is working it means that your FGCom is working, why do you think your FGCom is not working ?
The switch off/disconnect is expected: echo test is limited to 1 minute duration, after that you are automatically disconnected from the server because a "test" is not designed to be executed during a long time.
Keep in mind that FGCom is a communication system, in other words: if you are alone on the frequency there is nobody to talk with you. So if your definition of "not working" = "nobody talk to me" then I invit you to check that someone else is connected on the same frequency than you. You can check who is connected at
htp://fgcom.flightgear.orgRegards,
Clément