Mario,
If you have the DX configured to register to a gatekeeper, then you must make sure that the gatekeeper will allow the route to the call relay. You see, in telling the DX to register to the GK, you tell the DX to never perform any routing of its own. All routing decisions are to be made by the GK.
Without knowing your full application, I find in most cases you do not need to be registered to a GK.
MikeM
mike_voip@hotmail.com