You are correct, it never actually crashes. But after about ten minutes I decided to just close Ultiboard with the task manager. I've had this type of problem with Mutlisim as well, when loading schematics from previous versions. They eventually open if I let the program keep running.
If you save the bitmaps as a monochrome format, the gerber files are generated almost instantly. It took me about half an hour to figure out that the bitmap was causing the problem, I only found it because I realized it was pausing when generating the silkscreen layer.
