1. Check if you have enough empty space on the volume/drive you are downloading the library to. The Sonokinetic Manager will need twice the space of the size of the library to install correctly.
2. Press pause and resume button to force the Sonokinetic Manager to resume from it's current status
3. If you are downloading to an external drive, try downloading it to an internal drive. You can change the download path from the app preferences by clicking on the cog icon at the top of the manager and selecting a different download location.
If it still doesn't solve the problem, please share the sm.log file from the path given below.
~/Library/Application Support/Sonokinetic Manager