This took me too long to figure out, and was mentioned 3 years ago here.
If you have a build that errors with
# Error: 'Transform' object has no attribute 'inverseScale'
It’s because you have a node in the scene that clashes with a joint name you’re trying to create. In my case I had a piece of geo called head, and using the Epic naming convention which tries to create a head bone.
To fix: rename the geo/node clashing with your bone.