The trouble began when Anil wanted to shoot a scene in a particular way while Salman had a different opinion on that matter. They had a huge argument over this. The next time when Anil came on the sets, he saw that the action director, Tinu Verma, had already started shooting the scenes.
When Anil asked him to let him see the rehearsals and scenes that had been filmed, Tinu asked him to wait, since he was in between a shot. Anil lost his temper and so did Tinu and they fought as badly as Anil and Salman had.
Anil and Salman haven't gotten along well ever since Anil wasted time during the London schedule of Veer where, if he had been better prepared, he could've saved the budget from rising.
Tinu has confirmed the argument that took place between him and Anil but Anil doesn't seem to be very affected by this. He has passed it off as a light disagreement.