Why does Outlook want to delete this current meeting invitation, sent programmatically?

Question

I am sending meeting invitation mail via PHP to Outlook. Following code, i am using

BEGIN:VCALENDAR
VERSION:2.0
CALSCALE:GREGORIAN
METHOD:REQUEST
BEGIN:VEVENT
DTSTART:20150501T080000Z
DTEND:20150502T090000Z
DTSTAMP:20150511T075116Z
ORGANIZER;CN=Jass:mailto:[email protected]
UID:12345678123
ATTENDEE;PARTSTAT=NEEDS-ACTION;RSVP= TRUE;CN=Sample:mailto:[email protected]
DESCRIPTION:Complete event on http://www.sample.com/get_event.php?id=12345678
LOCATION: India
SEQUENCE:0
STATUS:CONFIRMED
SUMMARY:TESTING timezones
TRANSP:OPAQUE
END:VEVENT
END:VCALENDAR

Problem

When user receives mail then instead of accept and decline, it is showing Not current and when i click on it then it shows alert "This meeting request is out of date and will now be deleted"

What is the exact reason? I am not able to figure it out.

Answer 1

A couple of things:

1. Make sure an appointment with the same UID 12345678123) does not exist in your Calendar folder.

2. Make sure DTSTAMP does not contain a date in the future.