Please help me with this one issue - Kirupa Photo Gallery

Hi, I used K’s Photo gallery tutorial to make my own and everything seems to work well except for one issue. When I point the mouse cursor to the left or right of the thumbnail area, it will only scroll if I position it at the upper left and right corners. However, it does not move if in the middle or lower left and right areas of the scroller. The funny thing is that when I run the fla in movie mode everything works fine, but once I view it from the web server, no love… Any clues folks?