From: NedWebs on
It's possible that you have too many things animating at the same time. That's
the best I can offer without a better idea of what's going on in the banner.

Why are you using such a high frame rate? The Flash default is 12 fps, which
is kind of based on what the human eye can perceive (a compromise of sorts
since it can have somewhat jittery behavior). 30 fps is usually good enough to
get smooth animation.