Most often when your airbag warning SRS LIGHT comes on in your MERCEDES, it will be a Passenger Occupancy Seat Sensor failure
This fault can be described on diagnose same as bellow:
Child seat recognition seat sensor
Seat occupied recognition control unit
Passenger seat occupancy sensor
This can be a really expensive problem as the factory replacements can cost hundreds of Euro, plus the installation costs.  
There is also a safety issue as all airbags may be disabled.

We can supply replacement Emulators at a fraction of the cost for self installation - most of our device are equiped with original connectors- Plug&Play
Airbaglightoff Limited (Ireland) offer emulators for most Mercedes Benz cars on the market,
We are one of the  biggest supplier of these devices on the World

Check the list on the left to find one suitable for your car.