Yeah, certain MP3s are not encoded "correctly" and even if they play on WMP, mIRC doesn't like them. I've had a couple do that to me in the past and had to find different versions.
Of course, it is possible that in the last couple of versions, mIRC has gotten better at dealing with those. I haven't seen it happen since probably around 6.14. But I haven't seen any changes to splay either, so...
