I'm having problems accepting an appointment (C#). It's an existing appointment that the currently logged in user is invited for (So app.Personal == false and app.Accepted == false).

I'm using the class Appointment9...

When I call:

appointment.Accept();

I get:

System.Runtime.InteropServices.COMException was unhandled
Message=Accept not allowed on this message.
Source=Message.Object
ErrorCode=-2147352567
StackTrace:
at System.RuntimeType.ForwardCallToInvokeMember(Strin g memberName, BindingFlags flags, Object target, Int32[] aWrapperTypes, MessageData& msgData)
at GroupwareTypeLibrary.DIGWAppointment9.Accept(Objec t Comment, Object AllInstances)
...

But I have no idea why?? I also tried .Accept("Some text", false), but no difference.