Before you install any schema extension into your forest you should perform the following check to ensure a proper functioning forest is in place.
Verify Active Directory functionality before you apply the schema extension
Verify Active Directory domain controllers are online and that replication is functioning correctly before you update the schema to help ensure that the schema extension proceeds without error.
General Steps
1) Log on to an administrative workstation that has the Windows Support Tool Repadmin.exe installed.
2) Open a command prompt
a. change directories to the folder in which the Windows Support Tools are installed.
3) At a command prompt, type the following command
repadmin /replsum /bysrc /bydest /sort:delta
a. All domain controllers should show 0 in the Fails column, and the largest deltas (which indicate the time that has elapsed since the last successful replication) should be less than or roughly equal to the replication frequency of the site link that is used by the domain controller for replication. The default replication frequency is 180 minutes.
4) Determine Schema Master
a. At a command prompt, type the following command
netdom query FSMO
b. Record the domain controller name give as the schema owner
5) Verify that the schema master has performed inbound replication of the schema directory partition since the last time that the server restarted.
a. Type the following at a command prompt
repadmin /showrepl schema_dc
b. Where the schema_dc is the DC name returned as the schema owner from above.
c. Review the output for successful messages on the Schema container
CN=Schema,CN=Configuration,DC=domain,DC=com
Site_Name1\ServerDC1 via RPC
DC object GUID: 123ee243-1234-1237-1230-12319d4f27f4
Last attempt @ 2010-01-18 07:59:00 was successful.
Site_Name2\ServerDC2 via RPC
DC object GUID: 123cc9fa-1231-1238-123b-1233efbc5c80
Last attempt @ 2010-01-18 07:59:00 was successful.
Site_Name3\ServerDC3 via RPC
DC object GUID: 123889b7-123e-1230-1237-1230e6c2fe00
Last attempt @ 2010-01-18 07:59:00 was successful.
Site_Name4\ServerDC4 via RPC
DC object GUID: 123d6e08-1230-1232-1234-123adda6b953
Last attempt @ 2010-01-18 08:29:00 was successful.
Apply the Schema Extension
To install a Schema Extension a user must be a member of the Schema Admins group and the extension must be installed to the DC holding the Scheme Master role. Use the installation instructions included with the extension.
Verify the Schema Extension
After the schema is installed you should verify the schema extension’s are now included in Active Directory. This may very by product, but in general you should be able to use ADSI Editor to view the new schema objects or attributes.
Force AD Replication
You can now force AD Replication or wait for it to take place normally. Replication needs to occur before you attempt to use the product that requires the Schema Extension. Failing to allow replication to take place may result in errors being reported by the application.