that lot looks a bit complicated for your purposes - and I suspect there is information missing from the code you published here.
Why not try loading your external text in using the onClipEvent, then adding two simple scroll buttons with the most basic scroll commands:

on (release){
textfield.scroll--;
}

on (release){
textfield.scroll++;
}

where textfield is the variable name you have assigned to your dynamic text box.

on friendsofed.com you will find a book called php for flash (yes I know what you are doing does not involve php...). Download the free chapter (chapter 1) as a pdf. This has a little tutorial in it for loading dynamic content from text files. Also help with basic scrolling. Hope this helps,
Paul