Are you using iTunes 12.2 or 12.3?
If yes, please try this.
1. Please quit iTunes and the doubleTwist Sync application.https://www.doubletwist.com/help/question/guide-to-doubletwist-sync/#F
2. Search for all iTunes XML files on your system. The filename should be:
iTunes Music Library.xml
3. Please rename or remove all copies found.
* NOTE: Do not touch the "iTunes Library.itl" file as this is the actual iTunes library database. *
4. After renaming/removing the XML file, please launch iTunes. Go into the Preferences -> Advanced section. Make sure that "Share iTunes Library XML with other applications" is enabled. If it is enabled, try toggling it from on to off and then back to on to force the XML file to be created/updated.
5. A new "iTunes Music Library.xml" file should now be created.
6. Launch the doubleTwist Sync application and all of your iTunes playlists should now be seen correctly.
Otherwise, if you are using an older version of iTunes, here is a step by step sync guide. The initial section has information on how to remove/rename iTunes XML files and reset the doubleTwist library database to force a new import. You should get a "Launching iTunes" dialog during the process. If you do not, that would mean that the incorrect XML file is still being used.http://www.doubletwist.com/help/question/guide-to-syncing/#A