I got it running again by clearing the eeprom of the gateway and downloading the sketch of the gateway again.

sensor id is not the same as node id. sensor id = 255 is used for internal stuff like id request and battery level for node. You can assign 0-254 to your own attached sensors (to the arduino node).

@C.r.a.z.y. is this confirm? coz i'm having the same problem. and Yes, i'm using serial for my gateway and usb for my sensor. Please share if there's possible answer for this problem. thanks