iCloud's Calendar is full of errors and problems for me. The "Couldn't move your calendars to iCloud because an error occurred" is now gone (by itself) but nothing syncs between my Mac's Calendar to iCloud or my iPhone to iCloud.
I tried creating a new event directly on iCloud.com to see whether it pushes to any of my device and got this "This event couldn't be created because of a server error; please try again." error.
Apple, please fix this!!