Version:           1.9.6 (using KDE KDE 3.5.6)
Installed from:    Ubuntu Packages
OS:                Linux

After clicking on [Accept], [Accept cond.] or [Decline] an informational dialog shows with message "You must specify at least one receiver,either in the To: field or as CC or as BCC." and no notification email is sent. The meeting is sucessfully placed to calendar.
After kmail starts again a window with prepared notification mail is opened with subject "Answer: ..." and empty TO field.
I also tried to delete kmail and korganizer settings (from .kde directory) and reconfigure all again but with no help. Attaching the original invitation.

Content of prepared notofication mail:
BEGIN:VCALENDAR
PRODID:-//K Desktop Environment//NONSGML libkcal 3.5//EN
VERSION:2.0
METHOD:REPLY
BEGIN:VEVENT
DTSTAMP:20070430T115557Z
ORGANIZER:MAILTO:
ATTENDEE;RSVP=TRUE;PARTSTAT=DECLINED;ROLE=REQ-PARTICIPANT:mailto:
 m.zdila@company.com
X-MICROSOFT-CDO-IMPORTANCE:1
CREATED:20070430T115557Z
UID:
 040000008200E00074C5B7101A82E00800000000D0BB07981B8BC701000000000000000010
 000000628C05751BCA3F4F882A7E5539AD3513
SEQUENCE:0
LAST-MODIFIED:20070430T115557Z
DESCRIPTION:When: 30. apríla 2007 12:00-13:00 (GMT+01:00) Belgrade\, 
 Bratislava\, Budapest\, Ljubljana\, Prague.\nWhere: 
 Kosice\n\n*~*~*~*~*~*~*~*~*~*\n\n\n
SUMMARY:Epi Lunch
LOCATION:Kosice
CLASS:PUBLIC
PRIORITY:5
DTSTART:20070430T100000Z
DTEND:20070430T110000Z
TRANSP:OPAQUE
REQUEST-STATUS:2.0;Success.
BEGIN:VALARM
DESCRIPTION:Reminder
ACTION:DISPLAY
TRIGGER;VALUE=DURATION:-PT15M
END:VALARM

END:VEVENT

END:VCALENDAR