Check that the track names do not contain any special characters, for example Scandinavian or Cyrillic characters. This problem can appear in two situations: 1) You are using a phone that doesn't support all the characters you have used in track names, or 2) you have converted your music tracks to eAAC+ (.M4A) format. The eAAC+ format contains only the ID3V1.0 tag for track names and this supports only 7bit standard ASCII characters from a to z.