On the iRiver Hxxx devices, there have been reports that some tracks synced to the device do not appear on the device UI. This occurs whenever the '{' or '}' characters are included in a track's filename.
To fix this issue, edit the [FilenameMappings] section of MediaMonkey.ini file by adding the following two lines:
7B=2D
7D=2D
For more information about editing the mediamonkey.ini file, see:
http://www.mediamonkey.com/support/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=17