Ripping track information to HD

Hi - When I rip a CD to my Hard Drive after I have obtained the track information from the internet, I can only achieve playable mp3 files If I leave the Name Creation option to default. If I attempt to use either the Manual or User Defined options, whilst I get correctly named and numbered files on my Hard Drive (indicating I’ve got the ‘string’ correct) they appear as Unknown File Format without a ‘proper’ icon and cannot be played.
Any suggestion as to what is going wrong would be welcomed.

Thanks Peter