Fedora 7, Zimbra 5.0.1

I can create a "normal" one instance appointment in the shared calendar but when I try to create a recurring appointment I get;

msg: invalid request: Cannot create/modify an appointment/task with organizer set to user1@domain.com when using account user2@domain.com
code: service.INVALID_REQUEST
method: ModifyAppointmentRequest
detail: soap:Sender

I have changed the user and domain parts for this post.

Thanks all