Can I make a sprite sheet of a character which contains animated movies inside the main movie-symbol? I tried to export it, but those movies inside the main one are not animated. Thanks
Unfortunately I don't think you can do that. Even if you were to export the animation itself as a sequence of PNGs, nested animation doesn't get exported in Flash, and the same applies to sprite sheets.
You can export sprite sheets for the animated movies inside the main one and, as long as it doesn't rely on movie clips inside it animating, it will export fine. Only the first level animation will export.
Alternatively, you can use graphics instead of movie clips. Then from the top movie clip, select the frame the graphic should be in. Look for the options in the Looping section of the graphics properties.