Error: Call to undefined method DateTime::getDateInformation() (0)
#0 /home/myserver/public_html/forums/applications/calendar/sources/Event/Event.php(363): IPS\calendar\_Event::_findOccurances(Object(IPS\calendar\Date), NULL, Object(IPS\calendar\Date), Object(IPS\calendar\Date), Array)
#1 /home/myserver/public_html/forums/applications/calendar/sources/Event/Event.php(2127): IPS\calendar\_Event->findOccurrences(Object(IPS\calendar\Date), Object(IPS\calendar\Date))
#2 /home/myserver/public_html/forums/applications/calendar/widgets/upcomingEvents.php(153): IPS\calendar\_Event::retrieveEvents(Object(IPS\calendar\Date), Object(IPS\calendar\Date), NULL, 5, false)
#3 /home/myserver/public_html/forums/system/Widget/Widget.php(833): IPS\calendar\widgets\_upcomingEvents->render()
#4 /home/myserver/public_html/forums/system/Widget/Widget.php(888): IPS\_Widget->_render()
#5 /home/myserver/public_html/forums/uploads/template_45_94a9d7649fb9cdbfc784d3516e61a717_global.php(18472): IPS\_Widget->__toString()
#6 /home/myserver/public_html/forums/system/Theme/SandboxedTemplate.php(61): IPS\Theme\Cache\class_core_front_global->widgetContainer('sidebar', 'vertical')
#7 /home/myserver/public_html/forums/uploads/template_45_94a9d7649fb9cdbfc784d3516e61a717_global.php(15695): IPS\Theme\_SandboxedTemplate->__call('widgetContainer', Array)
#8 /home/myserver/public_html/forums/system/Theme/SandboxedTemplate.php(61): IPS\Theme\Cache\class_core_front_global->sidebar('right')
#9 /home/myserver/public_html/forums/uploads/template_45_94a9d7649fb9cdbfc784d3516e61a717_global.php(6862): IPS\Theme\_SandboxedTemplate->__call('sidebar', Array)
#10 /home/myserver/public_html/forums/system/Theme/SandboxedTemplate.php(61): IPS\Theme\Cache\class_core_front_global->globalTemplate('f1cc0e801d5818f...', '\n\n<div class='i...', Array)
#11 /home/myserver/public_html/forums/system/Dispatcher/Dispatcher.php(173): IPS\Theme\_SandboxedTemplate->__call('globalTemplate', Array)
#12 /home/myserver/public_html/forums/system/Dispatcher/Standard.php(113): IPS\_Dispatcher->finish()
#13 /home/myserver/public_html/forums/system/Dispatcher/Front.php(625): IPS\Dispatcher\_Standard->finish()
#14 /home/myserver/public_html/forums/system/Dispatcher/Dispatcher.php(155): IPS\Dispatcher\_Front->finish()
#15 /home/myserver/public_html/forums/index.php(13): IPS\_Dispatcher->run()
#16 {main}

This shows up repeatedly for all our admins. I already tried disabling all customizations and the problem persists. 

Go to the support page in your ACP and you should see optional patches available to fix this.

Thank you, Nathan. I've been trying to find the solution to that very same issue. Had to look fairly closely to find the "patch available" item. 

Glad to hear the issue was resolved for you 🙂

Thank you, seems to have fixed it.