Activate Schema Update Allowed Registry Key
By default, Active Directory is "locked" to prevent changes to the schema. After you identify the schema master server, you may need to add the following registry key before you can make the necessary extensions for segmenting Outlook Web Access.
Warning Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.
For information about how to edit the registry, view the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it, and you should also update your Emergency Repair Disk (ERD).
To activate the Schema Update Allowed registry key on the schema master server