Unsupported mp3 files?

When I playback some mp3 files from a USB pendrive on my Ematic AT103B Digital Converter Box, it plays some and displays Unsupported File error with others. As far as I know, they are all mp3 files downloaded the same way, and they all play fine on my computer.
How can I troubleshot this issue?

Get a program like Audacity (which is free), load the MP3 file in to it, then save it back out - MP3's aren't all the same, your converter box presumably only plays a selection of different types?.

Worked like a charm! Thanks a lot.

That was fast!!