I'm not sure if you fully understood the last post from trailman73. Make certain you're applying that registry update to the Windows 2000 Active Directory schema master server. You do not apply this to the CallManager, you apply it to a specific domain controller in your Active Directory domain, the one that holds the schema master FSMO role. You also need to point to that specific domain controller during the schema update portion of the Customer Directory plugin install process.
If you don't know which server holds this role, consult with your friendly local domain admin. If you are the friendly local domain admin and don't know which server holds this role, you can use ntdsutil or the Active Directory Schema MMC snap-in. The snap-in will not only tell you which server is the schema master, it also has a handy checkbox for turning on schema modification permissions, which is another way of accomplishing what you need to do if you're still having trouble with the registry entry. See the following URL for more info:
http://www.serverwatch.com/tutorials/article.php/10825_1468641_3
