The version I heard was that the Germans came to Oslo to have a meeting with the king, they asked for a no resistance surrender. The king did not agree to the German terms. The Germans and the king concluded the meeting, the Germans left and the king decided to flee. The next day he fled, the war started in Norway between the Germans and the Norwegians, not much of a war really since no one had been warned so there was no defenses up when the Germans came roaring up the coast in their ships and so on. This might be wrong, I've heard many different stories.