This topic again....lol
Okay. At the Tenkaichi Budokai, Gohan used "remnants" of his previous anger towards Spopovitch to tap into Super Saiyan 2. In the Viz manga, when he's trying to transform into SSJ2, you can clearly see him trying to get furious, which worked after a good struggle. No doubt in my mind the beating of Videl fueled his rage, as it was still fresh in his memory. However against Majin Buu, he said that he could not be the way he was then, which is a reference to his SSJ2 transformation at the Cell Games, where he was furious. So there you have it, even seven years post Cell Games, Gohan still needs deep anger and emotion to be the driving force, the trigger of his SSJ2 form, it's the only logical way to explain the statement he made prior to transforming into a Super Saiyan in front of Dabura and Babidi. A trigger, that was not present any more then.
In any case, the answer to the thread is obviously that he could not use SSJ2 at that point in time any more. The reason is factually unknown but I chalk it up to the having no access to it at the time, as it makes most sense to me personally...lol