WP Empire Builder: Error: "Custom post type 'XYZ' found in the export file is not defined on this blog" when trying to import content

If you try to import content with WP Empire Builder and you get an error like:

Error: Custom post type 'XYZ' found in the export file is not defined on this blog. Please install a plugin or theme defining this post type.

...then this means that you need to also install plugin XYZ on the network as well, so the blog that will "receive" the content can "read" what type of posts it receives.