On my "new" 2007 SL550 (only 13000 miles on it) I have frequent trouble using the CD Changer as it thinks the cassette isn't in place. I pulled the cassette and examined each tray, removed any rough edges on the sliding surface and wiped a bit of silicone lube on the surface. Now it kinda works in that I try it before driving and it might work but if I get that message, I eject the cassette and reinsert it and that usually will get it working and I can drive off. I imagine that the cassette is not exactly in place so the sensor doesn't reliably recognize it. Does anyone have any thoughts on this and know a way to adjust the cassette or the sensor for it?

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

Update: The changer now seems to be working reliably. I imagine that the silicone coating I put on the sliding surface of each tray has been transferred to its mating surface on the actual changer and the resultant low friction has done the trick. For the record, I used 3 in one silicone lube but a bit of Rain-X should work too.

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'76 240D-Sold
'78 240D-Sold
'85 300 SD, 165K-Sold
'88 300 TE, 165K-Sold
'64 Porsche 356C Cabriolet- under restoration
'86 560SL 124K Miles-Sold
'94 320E Wagon, 74K Miles-128K Miles JUNKED
'06 E350 Wagon, 84K Miles
07 SL550, 14K Miles

You can also, usually, just restart the car and it will work fine. (Happens to me on occasion.)

It appears to be an intermittent electrical quirk on engine starts.