Basically, Kurosawa was hired to direct the Japanese segments of the movie. His work was completely micromanaged by the studio, telling him how to direct and constantly undermining him. Since he was widely considered one of the greatest film directors EVER, he naturally took offense, at which point the studio began spreading rumors around Hollywood that he was "difficult" and "impossible to work with". When it got to the point that it was affecting his health, he quit the movie. Of course, that meant that the studio said it proved they were right, and since Kurosawa wasn't really in a position to defend himself, it seriously damaged his reputation, both here and in Japan, which made it much harder for him to get funding for his films. There were other factors too, of course, but he later said that this period was the worst of his life (he attempted suicide not too long afterwards). I have tremendous respect for Kurosawa-san (seeing "Ran" still takes my breath away), and so it's difficult to watch "Tora Tora Tora", although I will admit it is an excellent movie.
Sorry about how long-winded that was...my inner film geek isn't a pretty sight!
