This error can happen if your mobile device is not "application unlocked".
If you want to check if your mobile device is "application unlocked", please check out this page.

If your mobile is "application unlocked" and the error is still present after restarting your mobile device, please connect your mobile device, build a log archive with "Tools/BirdieSync/Archive logs..." (including the mobile device logs) and send it to support [at] birdiesync.com.