Hmm. After reading the paper it looks like it was a typical EGR problem with soot build up causing the EGR valve/system to malfunction.
The interesting thing is that this problem usually occurs when you use the car for short trips only, but that doesn't seem to apply to you ;-)
Not an uncommon problem it seems (scroll down this post) :
http://www.bmwforums.info/general-gu...html#post14989