iTunes Problem?

Several months ago I recorded a playlist from an internet radio station using Audio Hijack Pro and subsequently imported this into iTunes. Inexplicably I am unable to play this on either my iMac or iPhone. It is as if the file no longer exists, but it is still listed under Music within iTunes. I'd appreciate any help or advice.

If this should be listed within the "Music and Audio" forum please let me know and I will repost this.

Many thanks.