Two XPpro's each with Outlook XP. I used to be able to create a
Calendar item on one and send it to the other, and it was in the
proper format to be accepted and placed on the other calendar. But now
calendar invites are just being sent as Plain Text and cannot be
accepted - not even if sent to itself ... it appears as just Plain
Text
... but the actual text itself seems to contain the proper
vcalendar format as shown below:

Subject: Updated: Total Eclipse at 9:23
Date: Wed, 27 Oct 2004 20:00:26 -0500
Message-ID:
MIME-Version: 1.0
Content-Type: text/calendar; method=REQUEST;
charset="utf-8"
Content-Transfer-Encoding: 7bit
X-Priority: 3 (Normal)
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook, Build 10.0.6626
Importance: Normal
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180
X-Loop-Detect:1
Status:

BEGIN:VCALENDAR
PRODID:-//Microsoft Corporation//Outlook 10.0 MIMEDIR//EN VERSION:2.0
METHOD:REQUEST BEGIN:VEVENT ATTENDEE;CN="
(ROLE=REQ-PARTICIPANT;RSVP=TRUE:MAILTO:xxx
ORGANIZER:MAILTO:xxxnet
DTSTART:20041028T020000Z
DTEND:20041028T023000Z
TRANSP:TRANSPARENT
SEQUENCE:4
UID:040000008200E00074C5B7101A82E00800000000006EABE786BBC4010000000000000000100
00000D986966E42D7DC428F8EE1B3FD4AEC1B
DTSTAMP:20041028T010027Z
DESCRIPTION:When: Wednesday\, October 27\, 2004 9:00 PM-9:30 PM
(GMT-06:00)
Central Time (US & Canada).\n\n*~*~*~*~*~*~*~*~*~*\n\n\n
SUMMARY:Updated: Total Eclipse at 9:23
PRIORITY:5
CLASS:PUBLIC
BEGIN:VALARM
TRIGGER:-PT0M
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR