1)You cannot use the Exchange Management Console to create a new Autodiscover service virtual directory.
2)Before you perform this procedure, confirm that the Autodiscover service is disabled on the Exchange 2007 server. The Autodiscover service is disabled if the   Autodiscover service virtual directory is not present under the Default Web Site node in the Internet Information Services (IIS) console tree
New-AutodiscoverVirtualDirectory -Websitename <websitename> -BasicAuthentication:$true -WindowsAuthentication:$true