I had the exact same problem with my 3.0D.
Having spent almost a week at the dealers the problem resolution was as follows.
The fuel rail pressure sensor had become faulty and was telling the engine management system that there was insufficient fuel presure therefore it wouldn't start....but as with things that are faulty, it sometimes did start and run ok
So, there were no fault codes present as the management system was still receiving signals from the sensor - but they were wrong!
After a lot of time and money, the fuel rail pressure sensor was replaced (a cheap part) and all has been running well for over a year.
Hope this helps.