Startup Problem in i20 CRDi!

Made a thread on this issue yesterday morning, but it disappeared!! Doing it again. The Problem: The car refuses to start-up intermediately. The Background: 1) August 2009 model. 29000 kms done. 2) Last complete service (incl fuel filter change) : August 2011, 24500 kms. 3) Battery is brand new, bought last week. 4) Car is under extended warranty. 5) Fuel was taken only from the regular bunk, one I have been using for over 5 years. The Details: The car always starts up fine in the morning. After driving say 15 kms, if you turn the engine off, the car may or may not start up again. When stuck in "not starting" mode, the starter motor revolves, but the engine fails to catch. Even jump starting/push starting does not work. When the problem goes away, it goes away on its own. (Possibly by cooling?) When the car runs, it runs fine. No drop in power, no jerkiness, absolutely smooth. The A.S.S. The car has been with a A.S.S. for over a day. They tried diagnosing it with their scanners but everything showed OK. They managed to reproduce the problem once by driving it for 10-15 kms and then resting it for a hour or so. But their scanner still told them nothing. They are currently totally clueless. Another round of diagnosis is scheduled for 07.12.2011, but I don't have very high hopes. Help!!please:

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