How to enable schema updates on older windows 2000 DCs

Problem: Schema Admin group is not present or insufficient for write-access to Active Directory schema.

Cause: The extension or the modification of the Active Directory schema requires write access to the schema. This is enabled by means of the "Schema Update Allowed" registry key. Schema updates may be enabled by means of the Schema Management Console, or directly in the registry.

Prerequisite(s):

Windows 2000 functional level domain
Backup of registry before editing

Solution(s): Enable through registry.

To directly edit this registry key, perform the following steps: Click Start, click Run, and then in the Open box, type: regedit
Then press ENTER
Locate and click the following registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\Parameters
On the Edit menu, click New, and then click DWORD Value
Enter the value data when the following registry value is displayed:
Value Name: Schema Update Allowed
Data Type: REG_DWORD
Base: Binary
Value Data: Type 1 to enable this feature, or 0 (zero) to disable it
Quit Registry Editor

Verify updates allowed using Schema Diag utility tool.

Reference:

Schema Updates Require Write Access to Schema in Active Directory