Looks like bad coding in Yahoo! Messenger. I don’t use it enough (10 seconds a week?) to notice any problems in it. There is a number of reasons that this could happen, messenger isn’t releasing memory or handles assigned to a sound, or it does and tries to use the sound again and its already gone.
As for going off topic, I just felt an explanation was appropriate as I felt as though I was being told off for expanding on some points.