After changing the oil in my '99 CLK430 I was unable to reset the "Service Due Now" message that had been appearing for a couple weeks. I had previously been able to reset the service reminder message by following the instructions on page 93 of the manual (a page which I keep a copy of in the glovebox as I refer to it often) but this time had no luck. I stopped by the local M-B dealer to buy a couple parts, including a low beam light bulb, and had the service manager attempt to reset the message. No luck; he gave up. Got home, installed the bulb and BINGO! the display that had also flashed the message that the bulb was burned out now said "Service Due in 200 Miles". I was then able to reset the display at that point so that it correctly read 10,000 miles. So . . . . If you have a burned out lamp - or possibly another pending problem on the display, the display may not reset. And as a reminder - to reset the display, the doors have to be closed AND the electronic (not the valet) key used.