Events - Export to ical - error 500

Hi

I've just been informed by one of our members that "Export to ical" is giving an Error 500

500
LAYOUT EXPORT_SITEEVENTSDEFAULT NOT FOUND.
OH MY GOSH! YOU FOUND IT!!!
Looks like the page you're trying to visit doesn't exist.
Please check the URL and try your luck again.

I've no idea how long this has been happening as i personally dont use the export.

Any idea what could be causing this?

Thanks

Steve