I'm using music from the asset bundle provided by Scirra with the purchase of Construct 2. I'm inserting MattOglseby - 1 for the background music. I have it set preload and play on the start of layout (I've tried not preloading with no luck also). The music plays fine when I preview the game but once I publish the music doesn't play at all in Firefox, Chrome or IE. All other sound effects (non-music) work fine.
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After export try to check for errors on your browser, this should give clues as to what is going wrong.
Make sure your server has the correct MIME type (as specified in this manual article.
Be sure to refer to this manual article on how to use correctly music files in your project.