If the second keyfob can unlock the car over rf and the Crossfire runs with the first keyfob the Skreem has to be intact. On your first key is:
1. the batterie emty
2. the syncronisation with the skreem has lost (also when the batterie is emty and a new would be insert) to syncronize it in the Crossfire, close the door, press 5 times open or close on the keyfob, insert the keyfob within 2 seconds into the ignition switch and turn to the second position (lights in the dash goes on). If the turning signal in the dash blinks your remote is synchronized again.
3. the rf part is broken
and I think your second key has no transponder.
If in your first key the rf part is defective maybe the Skreemulator is something for you because you don't need to repair 2 keyfobs or buy 2 new. With the Skreemulator you don't need a Chrysler/Mercedes keyfob any more, only a mechanic key (without transponder) for the ignition switch. So both of your existing keys will work with it.