I get an error: "Syncing finished with error: java.io.IOException: Received authentication challenge is null".

This error message states that the username and/or password is incorrect. You will need to update this info.

1. Open Handheld Contact on the device.
2. Press the Android Menu button and choose Settings.
3. Click on 'Handheld Contact account'.
4. Update the 'User name' and 'Password' screens to the correct info.
5. Save changes and try syncing again.