There's an issue with installing SP1 for MotionBuilder 2016 if you already have MotionBuilder 2015 SP1 installed on your computer. It'll give this error:
If you try installing the service pack through Autodesk Application Manager it will give Error 1642.
We're working on a new version of SP1 for MotionBuilder 2016 that will resolve the issue. In the meantime, you can find a workaround for installing it here:
UPDATE: A new version of MotionBuilder 2016 SP1 has been released that resolves the issue. You can download it here: