In Windows Live Mail, sending and accepting meeting requests directly from the calendar interface is not supported as it was in previous versions of Outlook Express. Windows Live Mail is more focused on email functionality rather than advanced calendar features like sending meeting requests.
To send and receive meeting requests, you typically need to use a more advanced email client such as Microsoft Outlook. Microsoft Outlook provides more robust calendar features, including the ability to send and receive meeting requests with responses like "Accept," "Decline," and "Tentative."
If sending and accepting meeting requests is essential for your needs, you might want to consider transitioning to Microsoft Outlook or another email client...