EMBEDDING THUMBNAILER IN AN HTML PAGE
When a Flash movie (swf) is embedded in an HTML page, the external paths must always be relative to the folder where the HTML file is located, NOT the folder where the swf is located.
When testing your movie containing the thumbNailer in the Flash authoring environment, the path to the thumbnails may be "thumbs/", however if you embed the same file in an HTML page that's in a different folder to the swf, you need to change the thumbnail image path so that it will be relative to the location of the HTML page.