movie clip timings

[trh73]

Hi
I am a student making my first animation
When I preview my movie the timing of all my movie clips is out, this seems to get worse throughout the movie.
Also some clips appear and disappear.

I am not using any action script - just putting events on the timeline.

Any help would be great

[kumarr006]

your question is not clear enough to answer, pls describe it clearly.
thanks,