Xbox you say? It must be the disc. I don't see any other reason why that could happen.
Try getting it buffed at a local CD shop. They can get out scratches you wont see.
Other than that, try starting a new game. Going to Bruma, and using that gate.
If it works, then you did something in your xbox file that screwed it up. If it doesn't work. :confused:
But on the bright side it isn't nearly game breaking. If you dislike fast travel either
A. Use the other gate.
or
B. Fast travel when you are already at the gate.