stucks while changing frames, any reasons?

[still learning]

hi all,

i am working on a rough draft of "pitfall" like game. but my game stucks for a second while changing background screen. Why is this happening??? i m totally confused and afraid that after changing graphics which may heavier than those of now, it'll run very slow.

help needed urgently. do have a look on attached fla file to get the clear picture of my problem.

To administrators:-I asked that problem in the forum earlier also, but didn't get any response. May be the title fo the thread was not clear/related to the problem. So posting again.

pkk