Save a roster file on Madden to a USB.
Take out the USB plug into your computer.
Download Horizon and look for the roster file that you saved.
Copy down all the ID's down to a notepad somewhere.
(You will need to copy these IDs into the new roster file)
In Horizon, "inject" the new roster file that you downloaded here and paste in all the ID's that you copied earlier.
Save and rehash.
Now plug the USB into you 360 and load it up.