Fatal error: Uncaught Error: Call to a member function reject() on int

Overview of the issue

If you are using Memcached on your server and attempt to update WPML String Translation before the WPML core plugin, you see the following error:

Fatal error: Uncaught Error: Call to a member function reject() on int in …/wp-content/plugins/wpml-string-translation/classes/translation-files/Domains.php:132.

Workaround

Our developers are aware of this situation. In the meantime:

1. Access to your /wp-content/plugins/ directory via FTP.
2. Rename the wpml-string-translation folder. This will disable WPML String Translation.
3. Clear your cache server, specifically Memcached or Redis.
4. Update WPML to 4.6+.
5. Rename the wpml-string-translation folder to its original name.
6. Activate it from the Plugins page. The error should be gone.