Google appears to have fully resolved the issue at this time, further information can be found on the previously linked status page: https://www.google.com/appsstatus#hl=en&v=issue&sid=2&iid=cc21ebe3962430b2e4ae2b52e3dde98f

It appears Google has fixed the issue for some users at this time, they expect to have it resolved for most accounts within the next hour.

Google Calendar is currently experiencing a service outage affecting most, if not all users, you can find more information on this status page here: https://www.google.com/appsstatus#hl=en&v=issue&sid=2&iid=cc21ebe3962430b2e4ae2b52e3dde98f

We will pass major updates along here as Google provides them.