Silent error when importing articles

Hello,
I’m trying to migrate a site over using this plugin. There are features on the website that are paid-only with this plugin, but we do have many regular articles. When I try to import, we get:

<tt>
=== START import 2017-10-02 21:28:08 ===
Connected with success to the Drupal database
Drupal data found:
129 articles
18 pages
0 categories
0 tags

[WARNING] Your Drupal database contains users. You need the Premium version to import them.
[WARNING] Your Drupal database contains comments. You need the Premium version to import them.
[WARNING] Your Drupal database contains custom nodes. You need the Premium version to import them.
[WARNING] Your Drupal database contains custom taxonomies. You need the Premium version to import them.
[WARNING] Your Drupal database contains URL alias. You need the Premium version to import them.
[WARNING] Your Drupal database contains CCK data. You need the Premium version and the CCK add-on to import them.
Importing categories…
0 categories imported
Importing tags…
0 tags imported
Importing articles…
</tt>

at which point it stops working, and the “Start/resume the import” option reappears.

Thanks for any help!