To elaborate on what GodEater said: If you have "Auto Change Directory" turned on then you can easily end up playing a directory containing voice recordings if you created the original dynamic playlist by selecting a file in the file browser.
In any case, playing a voice recording in this way shouldn't cause any problems. If you are playing a playlist containing a path that doesn't exist anymore then Rockbox should just proceed to the next entry. I would check my player for file system corruption if I encountered this problem. (You can try chkdsk on Windows or fsck.vfat on Linux.)