Why it happens

The metrics engine, provider discovery and data-source logic live in that system plugin. Joomla only registers a plugin's classes for autoloading while it is enabled, so disabling it makes the component unable to load its engine - Insight now degrades gracefully and shows this notice (with a direct link) instead of a fatal error.

Fix

1. Follow the link in the notice, or go to System → Manage → Plugins and search mokonyxinsight.
2. Enable System - MokonyxInsight (and, for scheduling and REST, the Task and Web Services plugins).
3. Reload Insight - the notice clears once the engine is back.

If the plugin is missing entirely rather than disabled, reinstall the MokonyxInsight package.