Which object structure are you using? You should be using something like MXOPERLOC. That error at a glance is thrown when the LOCOPER record is being added and the owner MBO is not LOCATIONS. I'm not sure how that would happen because you normally wouldn't interact with this object directly.
Just a heads up, due to how application import works with a single commit, loading hierarchies would be complicated. You'd need to load the top level, then second level, then third level, etc. That's not the cause of your issue but it would probably be worth doing this as an Enterprise service import on the External System after you get past the issue.