Fatal error: Class 'WP_Requirements' not found

Hi,

Sorry you are having this issue. It is likely another plugin/theme that is conflicting. You can test that out with these steps: https://docs.simplecalendar.io/troubleshooting-theme-plugin-widget-conflicts/

We do have a way to combat this going forward though and will have an update for 3.0.13 for this issue. Hope this helps in the meantime!

When will the fix be live? And in the meantime can you post the code?

Thank you.

3.0.13 is live now, does it help with the issue for you?