Help for a Beginner: Why do my jitter videos keep freezing up? (Max 6)

Hello. I am not very experienced with Max, so please bear with me. I have about 10 videos that I would like to play at certain times, along with an audio going the whole time. I've finally hammered down the timing, but my videos keep freezing up. The first file plays just fine, but when it transitions to the next one, it only shows the first frame of the video the whole time. The same goes for the rest of the files (although the timing and transitions still work just fine).
My video files are compressed using Apple Motion JPEG to a .mov file. The largest file is 18 MB, aside from the audio file which is 64 MB (the audio plays just fine).
Any help on how to stop the freezing would be greatly appreciated! Please let me know if I should include any more information.

I am using a 2012 Macbook Pro with OS X 10.7.3 and 4GB Memory. I am using Max version 6.0.5.

Thanks again!
Jennie