Navigate to Songs (Music > Songs) and look at the alphabetical listing. At this level, you’ll see if any tracks are listed twice. I’ve had this happen when transferring an album to microSD card, then swapping to another player that has the same album in the internal memory. The songs on the card will show a wee card icon next to them.
If you transfer a track in MSC mode, then again in MTP, you can have duplicates, since from the PC, you won’t see both modes at the same time.
Lastly, if you use different audio formats or codecs, both versions of the song will list. For example, I can have an MP3 copy, as well as a FLAC copy of a song in memory (the e200 wasn’t granted FLAC capability, but the same thing will happen if one copy is WMA and the other MP3).