Keyless go not working


I have a 2008 MB S550 - the keyless go and push button start function has stopped working.  The key fob works in terms of locking/unlocking and starting with ignition.  However, the keyless go functions (locking and unlocking with handles, push button start) are not working.  When I try to lock and unlock with the handles, I can see the little red light on the key fob blinking but no actual locking or unlocking.