Actionscript Problem

I have a series of thumbnails that should scroll from left to right & right to left when you roll over the movie clip buttons on either side. IT was working in another flash movie, but I moved it to a different flash file and now it’s not working.

The hit buttons within the movie clip buttons have this action script:

on (rollOver) {
gotoAndPlay(“S1”);
}
on (releaseOutside, rollOut) {
gotoAndPlay(“S2”);
}
on (rollOver) {
if (_root.xkoord>-550) {
_root.xkoord -= 153;
}
}

That’s what is on the button on the right. I have no clue what “xkoord” is, can someone help me please? I am not much of an actionscript person.