I've added a change to support this, which also highlights more problems with Outlook 2003 - http://dnnevents.codeplex.com/WorkIte...

It may be we will need to drop support for Outlook 2003, since it does not seem to be able to accurately read .ics files according to the spec of RFC2445.

Cheers
Roger

One of the changes we made was to change from vCal to iCal (.vcs to .ics). iCal has greater functionality, including recurring event support, so I'm trying to get this going properly.

Roger

This error can appear if you have attempted to save a recurring Lunar appointment in iCalendar format.

To avoid this error, set the appointment option to Gregorian instead of Lunar.

And this is the exported ical file that downloads:

BEGIN:VCALENDAR
PRODID:-//DNN//Events 05.00.03//EN
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VTIMEZONE
TZID:DNN/LocalDST
BEGIN:DAYLIGHT
TZOFFSETFROM:+0000
TZOFFSETTO:+0100
DTSTART:20100328T010000
END:DAYLIGHT
BEGIN:STANDARD
RRULE:FREQ=YEARLY;INTERVAL=1;BYMONTH=10;BYDAY=5SU;COUNT=1
TZOFFSETFROM:+0100
TZOFFSETTO:+0000
DTSTART:20101031T020000
END:STANDARD
END:VTIMEZONE
BEGIN:VEVENT
UID:59
SEQUENCE:0
DTSTART;TZID=DNN/LocalDST:20100505T230000
DTEND;TZID=DNN/LocalDST:20100506T010000
DTSTAMP:20100504T152714Z
DESCRIPTION:http://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=Hylton+High+School&sll=37.0625,-95.677068&sspn=32.527387,78.662109&ie=UTF8&hq=Hylton+High+School&hnear=&ll=38.706946,-77.384949&spn=0.25023,0.614548&z=11&iwloc=A\n\n12u Crushers Outside Team Practice\nHylton High School JV Field\n
SUMMARY:12u Crushers Outside Team Practice
PRIORITY:5
LOCATION:Hylton High School
CLASS:PUBLIC
CREATED:20100503T000000Z
LAST-MODIFIED:20100504T040336Z
END:VEVENT
END:VCALENDAR

I'm running 5.0.3 of the Events module and DNN 5.1.2.