Creative Accounting.

Sometimes people in Hollywood are paid with a percentage of Box Office, DVD sales etc. The percentage can come off either the front end as soon as the movie is released or the back end after the film has made a profit.
Only a big star or director like Tom Cruise can get Front End. It's a well known thing in Hollywood that if you get Back end you'll never see a dime. Due to creative accounting, on paper almost no Hollywood movie makes a profit.
A while ago the man who wrote the Eddie Murphy movie Coming to America sued Paramount Pictures. He was supposed to get a cut of the profits and Paramount claimed a movie that pulled in over 400 million worldwide hadn't turned a profit?! The case got far enough along in the courts that certain people were freaking that Paramount might have to open it's books to the court. There was also people who could hardly wait to see this happen. If I remember correctly the case was settled out of court so Paramount never had to open it's books.
The moral is, if you ever get in a movie get the money up front.