Flash movies embedded in WebHelp project disappear or are black squares

When I embed a couple of small Flash movies (one .flv and one .f4v) into a help topic, the movies play fine when previewed from within RH or when I manually navigate to the SSL > webhelp directory and open the project with a browser. Leaving that environment (either installing our product and its help elsewhere or manually copying the help directory), the movies are either absent or show as black squares. All of the many environments we tested have the latest Flash plug-ins present. I've even verified that the Flash movies in the help directory play if opened manually in a player app.

What could be unique to the development environment that would allow me to manually open the webhelp project with a browser and play the movies with no difficulty yet that same directory, when copied elsewhere, fails to play the movies?

Many thanks!