I upgraded WordPress/EventEspresso and now I get an error “item_name” required.

This error may happen when the EventEspresso module did not initialise correctly. In some cases the “*_event_attendee_cost” table was not created, causing the SQL that fetches the item_name to break. To solve this, you just need to deactivate, and then reactivate the EventEspresso plugin. This will reinitialise the plugin, and recreate the table. Other tables will remain untouched.