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.
It hasn't worked since January 5th. So you are not alone. But you can use OpenSCAD instead. Install, open the .scad file and customize. You can download the latest version 2018.01.06 from the Development Snapshot section that has a customizer option, available under Edit > Preferences > Features > customizer.
OpenSCAD has a better preview and is much faster!