Problem with transitions in Imovie

[sweepstop]

I am making a movie with Imovie HD (6.0.3), and have used transitions successfully for a while, but all of the sudden, transitions refused to render (the bar would show, but there would be no progress on it, no matter how long you wait). If i add new photos w/ the Ken Burns Effect, they will still render, but it wont let me add new transitions. Any help would be appreciated.