This error message means some of the other applications using your device then this blocks the update process.
This is OSX right?
Most of the times the users who experienced the same issue it had Native instruments application installed on the computer and that application blocks the update.
It seems if the user force to close all of the running apps on the MAC that helps to free up the USB driver in this cause the updater starting properly.
Please follow this instructions:
0. Reboot your MAC, leave the LP-16 connected
1. Please find and start the “Automator” app in your launchpad.
2. Choose the “Application” in the Automator
3. In the search field type “quit” then select “Quit All Applications”
4. Make sure the “Ask to save changes” checkbox selected
5. Command + S –> or “File” -> “Save” name your application “Quit all applications”
6. Run that Quit all apps then start the USB updater