Flash anim runs different to site anim

i have an animation that runs differently to the same one uploaded to a site. i am using flash cs3 and have developed a conveyor belt type animation. action script controls everything about it. when i run it in flash i can leave the animation on for hours and come back. the animation runs just like i just started it. on the website the same animation has movieclips out of position. not by a great amount but enough to show that it is not running like the version inside flash.

how can this be? is it to do with the codebase?
this is the address: http://www.hamleys.com/Outdoor_+_Hamleys_Toys/090000000,default,sc.html as you can see once you run it long enough you will see a bigger gap form. its supposed to be seemless. infact it is when i run it inside flash

any help on this would be great