Imovie HD suddenly jumps/skips/freezes after many successful changes
I have a one hour video which is almost finished. But, after making many successful changes I suddenly find that any new change will cause the movie to get stuck on one frame, and then jump to another futher down. Sometimes the sound will move correctly, but the picture on my screen does not change. When this happens, the start/stop button on the screen does not respond to commands, and sometimes the pinwheel will appear.
I have corrected the permissions, done the drive repair, done the P/Q P ram clearing function, and Apple had me trash the Imovie Plist and cache to no avail. I had this problem once before with the Imovie that came before Imovie HD and I changed the hard drive at that time, so the drive is ok and I also get the same result when i use the external drive.
This only happens one hour videos with many changes. I have 1.5 Gb of memory. could some of the memory chips be defective? your help will be appreciated.
powermac G5, Mac OS X (10.3.9)