Gallery w/thumbnail Scroller, thumbnails load in same spot

i’ve followed this tutorial and when trying to recreate it from scratch on a bigger canvas my thumbnails all seem to load in the same spot even though i have placed my boundaries mc’s to the left and right of my mask. what am i doing wrong?

my canvas size is about 950x400.

it seems to work when the scroller is on the very left side of my background. But when i move the boundaries, mask and movie clip to the right side of my background it either dissappears completely or all loads in one spot.

i haven’t changed any of the // thumbnail code

please help