Thanks, Jetstream, I was just verifying that myself.
Schack, it is plain that you're in the right forum. I no longer have my '00 (similar to the '01) to check how to activate the child safety system for the rear doors; I did check an electronic version of my '00's operator manual and didn't find that either. However, the child safety feature, while disabling the inside handle, left the outside handles operable. You could have a malfunction in that feature.
You can manually unlock the door by pulling the door lock knob up. If pulling it up once doesn't clear the problem, try it several times. If you can get the door open with the exterior handle, then you can obviously check the child safety feature.
There is a fuse diagram for the U.S. specification cars posted at post #3, http://www.benzworld.org/forums/w220...e-diagram.html
(double click the diagram to enlarge it; zoom in, or save it to your desktop and open it with a photo editor so you can enlarge it further). Note that there are a total of five fuses for door locks - one for the central locking system, and one for each door control module. I cannot see how fuses would be your problem, since you say your door locks all operate - but give them a check.
Your interior and exterior door handles are mechanical, but they are connected to both electronic, vacuum, and possibly mechanical systems (the latter especially with your car's child safety feature). However, on my '05 W220, the child safety feature of disabling the rear seat interior latches definitely works with the rear window/rear lighter override feature. With the safety feature activated from the driver's window control panel, once the doors are locked, the rear doors cannot be opened from the inside.
Your car may not be U.S. specification, but to the extent it will help, you can download the Owner's Manual for many models and model years at Mercedes-Benz - Home of C, E, S, CLK, CLS, CL, SLK, SL, SLR, R, GLK, M, GL, G Class
- while the '01 and '02 S-Class are not available, the '00 S-Class manual is - and there are very few differences between those years in terms of operation.
You can also subscribe on a day-to-day basis to the Mercedes tech data (in English) at http://www.startekinfo.com/StarTek/
- perhaps something there will help.
Sorry I couldn't do more.