It could be frozen moisture inside the locking mechanism/inner door. I've had problems with my lock(s) several times on and off during cold snaps.

Best solution I've found is to park the car inside a garage somewhere and use a hair dryer to dry the affected area. This usually works wonders. You need to remove/evaporate the moisture trapped in there, which is likely causing the problem.

My driver's door lock wasn't working for the past few months. Nothing could fix it - tried lubing it, drying it, brought it to my mechanic who opened it up and also couldn't fix it. Then the other day I tried it just for fun and it worked perfectly...so go figure.

Good luck...

__________________
Chris
2007 E550 4Matic - 61,000 Km - Iridium Silver, black leather, Sport package, Premium 2 package
2007 GL450 4Matic - 62,000 Km - Obsidian Black Metallic, black leather, all options
1998 E430 - sold
1989 300E - 333,000 Km - sold
1977 280E - sold
1971 250 - retired

"And a frign hat. They gave me a hat at the annual benefits meeting. I said. how does this benefit me. I dont have anything from the company.. So they gave me a hat." - TheDon