The base directory you're working from is (something like):
[...]\Codemasters\OperationFlashpoint\Users\[Your Name]\missions\[Your Mission Name]\
Therefore, you're trying to play the file:
[...]\Codemasters\OperationFlashpoint\Users\[Your Name]\missions\AddOns\mymap_Anim\intro.Map\music\mytrack.ogg
Does this file exist? It doesn't look quite right if you ask me...
Why not try changing the line where the sound is defined to:
sound[] = {music\mytrack.ogg, db+10, 1.0};
Hope this helps,
Pope Zog