I've been looking for a tutorial on this subject, and I wanted to thank you for posting it here at TDC.
I've noticed one strange bit in the example EXE you enclosed: when close to the corners of the map, the screen shaking doesn't happen. I don't have MMF2 on the computer where I'm working now, so I can't have a look at the MFA myself. But what might be causing that issue?
There is nowhere to scroll when you are too close to the edge of the frame. You should leave some place for the "shake". Just put black backgrounds there.