Fatal error

I was able to import data correctly a week or so ago but now i am getting a fatal error. I am using the same spreadsheet as previously.

Fatal error: Uncaught Exception: DateTime::__construct(): Failed to parse time string ({Conv. Date}) at position 0 ({): Unexpected character in /home/s2dp5yjzt650/public_html/wp-content/plugins/this-day-in-history/tdih-list-table.class.php:219 Stack trace: #0 /home/s2dp5yjzt650/public_html/wp-content/plugins/this-day-in-history/tdih-list-table.class.php(219): DateTime->__construct('{Conv. Date}') #1 /home/s2dp5yjzt650/public_html/wp-content/plugins/this-day-in-history/tdih-list-table.class.php(339): TDIH_List_Table->date_add_era('{Conv. Date}') #2 /home/s2dp5yjzt650/public_html/wp-content/plugins/this-day-in-history/tdih-list-table.class.php(179): TDIH_List_Table->item_add_edit() #3 /home/s2dp5yjzt650/public_html/wp-content/plugins/this-day-in-history/this-day-in-history.php(401): TDIH_List_Table->process_action() #4 /home/s2dp5yjzt650/public_html/wp-includes/class-wp-hook.php(292): tdih_display_list('') #5 /home/s2dp5yjzt650/public_html/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters('', Array) #6 /home/s2d in /home/s2dp5yjzt650/public_html/wp-content/plugins/this-day-in-history/tdih-list-table.class.php on line 219