When you have errors similar to the following

Warning: C_Calendar::loadAllCalendars(): It is not safe to rely on the system’s timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. 

It’s likely that the system timezone isn’t enabled.

Here’s an instruction how to set the timezone in php.ini in cPanel. If you don’t have cPanel, you can always open in any text editor and edit then save.

Always remember to restart web server after edit php.ini.