I've scoured the Internet, and found virtually nothing on this topic.
Hopefully this thread will help others out there. This problem is undoubtedly not limited to the W211.
Anyone with that has has Keyless-Go, and the door fails to latch, may find this information useful.

My 2008 E320 Bluetec developed a problem where the rear driver side door would not latch.
After taking the latch out, and taking it apart, I was able to figure out what's going on.
This solution only applies if your car has Keyless-Go, and the door fails to latch.

The door latch can be released three different ways. The internal door pull, the external door pull, or with Keyless-Go.

The external door pull and keyless-go door pull APPEAR to be the same, but they are actually very different things.
When the car is UNLOCKED, and you pull the door handle (internal or external), it's a mechanical lever or cable action that releases the door latch.
When the car is LOCKED, and you pull the outside door handle (with Keyless-Go), you're really actuating an electrical contact switch in the door handle. Assuming the key fob is in the proximity of the car, that contact switch causes a motor to spin and rotate a gear 180 degrees. The gear has a CAM on it that moves a lever to release the latch. After the door releases, NORMALLY the gear/CAM unwinds back to it's home position. (When activated it winds up a coil spring which then causes the gear/CAM to unwind when power is removed from the motor).

The problem is that if the CAM rotates 180 degrees and then "sticks", the door will NOT latch. It's just like as if you held the internal door pull in the fully extended position.

My CAM/gear was stuck in the fully engaged position. I applied 12V to the motor manually a few times to simulate activating Keyless-Go, and it finally unwound like it it needed to. After it unwound, the latch started to work as expected.

If the coil spring is broken, the CAM will never return to home position, and the door will not latch. You'll need replace the latch.
In my case, the spring was fine. I added an extra bit of preload to the spring, lubricated everything, reassembled and reinstalled. The latch works just fine now.

If you have this problem, you can try activating that door's Keyless-Go a few times to see if you can get it to unstick. This is handy to know if you are on the road and unable to pop the door panel.
If not you will need to remove the door panel and then remove and replace/fix the latch.



Keyless-Go release motor

 

Thanks for the info on that I am currently having the same problem, Hopefully I am having the EXACT SAME problem and am able to fix it. on my 04 E55 AMG w211....
The passenger side front door won't latch shut, I just put the old actuator back in the door yesterday after the car was involved in a passenger side accident. The Body Shop guys failed to put the old Hardware from the old door into the new door. Before i had put the old actuator back on, the door would Only open from the outside, but opened and closed normally and locked and unlocked normally just as long as you're using the outside handle (only outside door handle would open the door) So now that I put the new actuator in the door, you can open and close the door using either handle but it will only close and stay shut if the door is locked. I will repost this fixes my problem... thanx if anyone else har info...