It loads but it hesitates

i made an animation and put a loader in it.When you log on to the website it loads ( i also checked if it loads the swf’s size right yeah it does) but while animation is played it hesitates.But when you refresh the page the anime plays right because it is loaded from cash.I think i am having problem with my loader but i have used it many times and a problem like that never occured.So what can be the problem?