Problem with ScrollPane component and long list

I have used the ScrollPane component a few times and had no problems, but have run into a strange issue.

I have a long text list to scroll through that I created as a movie clip. When I test the movie, it shows part of the list, then the rest of the space is just white space, even though the scrollbar shows there is much more there.

Is there some kind of height limit to a movie clip I am not aware of? Any solutions?

Many thanks.