Scroller issue

This may be a flash mx > flash mx 2004 conversion issue I don’t know but the scroller is not working properly. I have a dynamically loaded set of thumbnails that I load into a movieclip and a set of scroller buttons. It worked before but somthing changed and now when I scroll down the thumbnails vanish and when I scroll back up they reapear.

Could someon please take a look at this and let me know what you think.

Thanks

http://www.zephn.com/kirupa/scrollertest.zip