MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
I think I just now fixed the file.
It means it's got a hole/non-manifold, 'cause it worked OK with my slicer at the time and I didn't know to check for those things.
I imported it with 3D Builder, let it repair the file, and then re-exported, I think it should be good now.