Same problem here.
We use Events Calendar for other clients in the same setup. This time, new install, it won’t save any details other than the name and content.
Not the venue, not the dates, not the times.
Confirmed – seeing this error on many, many sites.
Rolling back now.
Error is displayed as above with PHP 7.0.11, and in a shorter form with PHP 5.6
Close – Opcache in PHP 5.6. Clearing the cache after the upgrade removed the error.
