Blackberry File Invocation

Why this won't work on a device but it works on a bb simulator. Do you have any su开发者_开发百科ggestions to make it work on the device?

   Invocation invocation = new Invocation("file:///SDCard/BlackBerry/music/song.mp3"); 
   Registry reg = Registry.getRegistry("net.rim.device.api.content.BlackBerryContentHandler");
   reg.invoke(invocation);

I found the solution by registering not the content handler but the application package. In my case:

Registry _registry=Registry.getRegistry("myapp.mobile.app");