For whatever reason, the file(s) you are testing are not being supported by mIRC (assuming you *are* using the correct *full* path when calling the file). There have been various mp3s that I've tried playing in the past that work fine in WMP, but actually crash mIRC. I'd imagine it's a codec issue, but beyond that I don't know which one(s) you'd need. I'd try just updating to the latest WMP version and see if that helps. For that matter, I'd update your mIRC version as well. It's really old.
