Evt_media_loaded not working on vista/windows 7

For some reason the evt_media_loaded is not being triggered on my
windows vista and windows 7 machines. I use this so that I can auto play
audio, and as soon as it’s loaded I can play. I also have a windows XP
machine where it works just fine using the exact same code. Is there
anything I can do to fix this, or is there any way around this?

Right now I have it wait .5 seconds before trying to play the audio
file. But it may take longer to load different files based on size, and
also sometimes users play remote files on servers, so there may be a
slow connection.