Okay so I deleted the offending files from the directory and reconverted from WMA to MP3, etc, using an hour of my time. Reinserted to my external drive having this time retagged in music monkey (same error message on first attempt) and guess what - same error message - A Zero Sized Frame Is Found.
Why not just say - Blah Blah Blah Blah Blah, I am a tempramental bottom head as every other known media player in the world is fine with your MP3 conversion - Blah Blah Blah Denon is Paris Hilton.
Any ideas HD2500 users?