Thanks! I was trying to find this plugin earlier to see if it was current. It seems to be though responses are a little sparse from the developer.
I did a quick google search of this message "wp-content/plugins/all-in-one-event-calendar/all-in-one-event-calendar.php" and I saw this thread:
https://wordpress.org/support/topic/all-in-one-event-calendar-update-11011/page/3?replies=71 from 7 months to 4 months ago. Also this one:
https://wordpress.org/support/topic/fatal-error-cannot-use-object-of-type-stdclass-2?replies=21
These indicate it is a problem with the developer of that plugins code. Hopefully one of those solutions will be able to help.
tim