iCal Export Addon stopped working

My iPhone Agenda App can’t validate the iCal link anymore. It stopped working all of a sudden so I tried adding it again. When I use a ical validator it finds two errors:

• This is not an iCalendar file or URL near line # 1Reference: RFC 5545 3.4. iCalendar Object
• Missing VCALENDAR object near line # 1Reference: RFC 5545 3.4 iCalendar Object

What to do?

Thank you!