5 --> MX won't convert

I have this movie that creates elastic strings between movieclips the user can drag and stretch, but when I publish the file as Flash MX, something in the Actionscript is specific to Flash 5, and so the elasticity and drag functions are lost. I didn’t create this movie - I found it on Flashkit.com.

I never did understand the code much more beyond being able to pinpoint which values would alter the strength of the elasticity, so I have no idea where to look in order to find out what it is in the code that’s not MX-compatible. I need it to be in MX in order to use the many features MX supports.

I have attached the .fla.