Thank you very much for your reply. I have removed all the updatestage scripts as well as the repeat while scripts. I tried to control all the graphics form the sprite properties and not with scripts. The tempo is constant to 30 fps and I don't have any flash or videos in the movie. Now the graphics are always at the right position but still some times (randomly I think) it looks like the script hasn't been loaded and there is no functionality at the graphic.
When you say that mac/shockwave doesn't like the repeat while script is it possible to block the whole script (eg on mouseup) or just the part of the script (eg repeat while...)?