Problems in invites getting added to Calendar

We are generating the Lotus Notes Invite through a code ,and the invites are generating and being succesfully mailed to the client ,but when the client is accepting the invite ,it i snot getting added to the Calendar.What can be reason.below is the format of the invite which is generated by the code

BEGIN:VCALENDAR

X-LOTUS-CHARSET:UTF-8

VERSION:2.0

PRODID:-//Lotus Development Corporation//NONSGML Notes 7.0.1//EN

METHOD:REQUEST

CALSCALE:GREGORIAN

UID:20071001T143326Z-uidGen@phuseh-l51211.NA.novartis.net

BEGIN:VEVENT

LOCATION:Building: 105 Room: 2131

DTSTART:20080428T123000

DTEND:20080428T124500

TRANSP:OPAQUE

SEQUENCE:0

SUMMARY: AV 105-2131

ATTENDEE;ROLE=REQ-PARTICIPANT;PARTSTAT=NEEDS-ACTION;RSVP=TRUE:mailto:arnab.bhar@novartis.com

CLASS:PUBLIC

DESCRIPTION:Requestor’s Details:

ORGANIZER;CN=nilanjan.lahiri@novartis.com

UID:85DCF086D63D535E8525738B0077D408-Lotus_Notes_Generated

X-LOTUS-BROADCAST:TRUE

X-LOTUS-UPDATE-SEQ:1

X-LOTUS-UPDATE-WISL:$S:1;$L:1;$B:1;$R:1;$E:1;$W:1;$O:1;$M:1

X-LOTUS-NOTESVERSION:2

X-LOTUS-NOTICETYPE:I

X-LOTUS-APPTTYPE:3

X-LOTUS-CHILD_UID:85DCF086D63D535E8525738B0077D408

END:VEVENT

END:VCALENDAR