Tried both deleting the key and reactivating, even deleted and re-installed. Still no luck. I will try on another site to see if it's a theme conflict.
Discussion
There is a new version now (0.7.1) both at Github and also in the WP plugin repository. You can install nostrtium from the WordPress repo like any other plugin. Please let me know what you find. Maybe post an issue on github (https://github.com/pjv/nostrtium/issues).