Hi @krzysztofzpom
Glad you reached out.
From your first screenshot, it shows an issue with the Events Calendar plugin not being properly installed.
The screenshot also displays an error from a third-party plugin integrating with the Events Calendar called ‘Duplicate TEC Event’. This third-party plugin can causes issues with the latest release of the Events Calendar. That plugin has not been updated in over 5 years and is not affiliated nor support by The Events Calendar.
During the last few years, the Events Calendar plugins have gone through some major updates, including retiring legacy code affecting calendar views, and now a whole new events system with an improved backend to help with performance.
The latest version of Events Calendar 6.0 includes a feature to duplicate events within the WordPress dashboard. Check out our guide on Duplicating Events.
We recommend deactivating third-party plugins that may not be compatible with the Events Calendar. This should help you properly install and update our plugin. The event migration should work afterwards.
The second screenshot I’m not sure of or why that message would display but it may clear up once you resolve the above.
Thanks
Rob
