Mercedes Benz repair: keyless entry, dead car, c280

Question
1997 C280.  Key-bob (?) will not lock/unlock doors.  Batteries have been changed.  Key will lock/unlock doors from passanger door and trunk, doors will lock and unlock from switch inside.  What can I check?  Thank you

Answer
Best guess:
Corrosion within the key-fob, or alarm module is failing.
If I recall your system correctly, and it is the alarm module, when it fails for the last time it will go into engine kill mode = dead car.
Your local MB dealer can diagnose and repair either issue quickly.