Request attende answer (.vCalendar) C#

[Evelyn]

I've created an ASP.NET application where I can send meeting requests to
people. My code is based on the following example:

http://weblogs.asp.net/bradvincent/archive/2008/01/16/creating-vcalendars-programmatically.aspx

Sending and receiving the mail (outlook 2007) is working well; but there is
a problem:

When receiving the e-mail it's possible to accept/reject the mail, but no
e-mail is send to the organisator. Furthermore it's not possible to edit the
answer before sending.

Does anyone know what I have to set in my vCalendar, to force the attende to
answer my request.

Thanks in advance,
Evelyn