The TypoScript setup variable plugin.tx_seminars.showAttendanceFieldsInNotificationMail contains the value "title", but only the following values are allowed:
(uid, interests, expectations, background_knowledge, lodgings, accommodation, foods, food, known_from, notes, checkboxes, price, seats, total_price, attendees_names, kids, method_of_payment, company, gender, name, address, zip, city, country, telephone, email)
These values specify the registration fields to show in e-mails to organizers. A mistyped field name will cause the field to not get included. Please fix the TypoScript setup variable plugin.tx_seminars.showAttendanceFieldsInNotificationMail in your TypoScript template.
The configuration check for this extension can be disabled in the extension settings in the backend: Admin Tools > Settings > Extension Configuration