I'm wondering the same thing as Carlos...Anyway, disabling the alarm would not be the solution, because the engine control system requires a signal from the security system to start from the CAN data bus.
I have a 1996 500sl with the same problem. The owner's manual says that if you inadvertently push the lock button on the key as you are starting the car it will enter the "lock out" mode. You are supposed to be able to click it again to back out of that mode and start the car but mine is not getting out of lock out mode and I can't start my car (it just turns over but will not start and the red and green lights blink simultaneously.
Please let me know if you figured out how to deal with the problem.
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