Last night the Google API (version 3) daily limit for CCal 11 was reached at about 11pm (NZ time) after only 4 hours after the daily limit counting started.
The restriction will lift at 7pm (NZ time) today. Until then, unfortunately, users can't sync.
Daily limit time starts at 7pm NZ time ( 0.00am San Francisco time).
Google can increase the daily limit at our request, (which we have already done), but it takes Google several weeks after reviewing the request to change the limit (we have already experienced this with another app).
Google have set up a paid option for some of their other services. For example, they charge a fee to developers who want to use map API over the limit, but there is no paid option to increase Calendar usage limit. (We can't pay to expand daily limit.)
Many CCal 10 users have changed to CCal 11 at about the same time and so Google has been inundated with requests. Usually after a few days, users will not sync as much as they do now, which reduces daily usage.
Unfortunately, at the moment, there is nothing you and we can do except for syncing before the daily limit has been reached.
CCal 10 uses API version 2, which does not have a daily limit. However, Google has stopped developing that API.