When playing MP3 from cache, Firefox displays "File not found"

The call to my script should play audio in your browser like audio/mpeg

.

Sound plays in Firefox under strong lighting, but no sound on second call.

The script tries to set Cache-Control

to stop caching. However, the browser seems to be caching and unable to receive audio content.

On the first call, my browser gets:

HTTP/1.1 200 OK
Date: Thu, 08 Mar 2012 20:21:16 GMT
Server: Apache
X-Powered-By: PHP/5.3.8
Cache-Control: public, must-revalidate, max-age=0, max-age=86400
Pragma: no-cache
Accept-Ranges: bytes
Content-Disposition: inline; filename=627.mp3
Content-Transfer-Encoding: binary
Content-Length: 16299
Last-Modified: Wed, 22 Feb 2012 21:58:33 GMT
Expires: Sat, 10 Mar 2012 20:21:16 GMT
Keep-Alive: timeout=5, max=100
Connection: Keep-Alive
Content-Type: audio/mpeg

      

        
        
        
      

    

On the second call, it gets:

HTTP/1.1 304 Not Modified
Date: Fri, 09 Mar 2012 20:21:54 GMT
Server: Apache
Connection: Keep-Alive
Keep-Alive: timeout=5, max=100
Expires: Sat, 10 Mar 2012 20:21:54 GMT
Cache-Control: public, must-revalidate, max-age=0, max-age=86400
X-Pad: avoid browser bug

      

        
        
        
      

    

... and no sound is played.

Any clues as to why this sound isn't playing on the second call?