ben, this is a "logic" question I think.  both are mp3 files, what can be difference?  size, bitrate, id3 tags, etc..  I don't think the size matters because 衛蘭's songs have difference size and they all can be played in wmp.  I think the id3 tags are the most suspicious

That's weird.  I can install wmp to test, if you want me to.  Or maybe I can download another version of 李克勤 (If i can find one.)

ben, oh if you don't already have wmp that's fine.  is there a way you can check the song tags (title, album name, etc.) and the properties such as bitrate?

Bit rate is: 320kbps, Encoded by: iTunes 10.0.0.68

all 李克勤 has that same settings?

Yes.

ok hold on a sec, let me find another "bad" file for you to check.  

in the meantime can u check 衛蘭's properties?

They all 320, but no info on Encode by.

hmm.. GEM playlist not work on iEar but it plays in wmp.  So the two problem might not be related.  I think we can focus on what do they have in common for haken and gem's songs, and what difference do they have comparing to 衛蘭's songs