Joseph Chan , Oct 10, 2009; 06:23 a.m.
When was the last time you opened it? It's possible the foam light seal around the back has deteriorated and become sticky. When you pull the film rewind knob up you should feel the spring resistance and most likely the door catch is being released. Try pulling the door open at the same time and seeing if it is just stuck by the foam.
If it is the foam, it's time to replace it!