Hey, Ian! I would like you to take a look at some MP3's that won't play in XMPlay. They do work with Winamp. I took a look at them myself, and I think the problem is in the ID3v2 tag. It's weird long and our player does not recognise the file.
They are named hack sign ost *... (Due to my connection restrictions I had to truncate the files to 128KB. But it doesn't make any difference: Winamp plays, XMPlay doesn't.)