The security code needs to entered but the number of retries has been exceeded there is a period of time with the key on engine off that needs to pass before the radio will reset so the code can be entered again
First, get the radio code. It is a five digit code located on a business size card in the original owners manual. If you don t have it you will have to make a trip to the Mercedes Benz dealership to get the radio code. It is based on the VIN and they can run it for you.
Once you have that code, turn the car and the radio on. Once you do that, a solid WAIT message will appear on the radio panel. Leave the car and the radio running for about 20 minutes or so. Some others have experienced longer wait times. The basic thing is that the radio has to be powered up and running. After 20 minutes (give or take some time) the WAIT message will change to a flashing CODE message. At that point, input the five digit radio code on the radio panel (using the preset keys 1-6) then press the SC button on the radio. That s how you enter the code. You may or may not have to turn the radio off and then back on.