SCCM Schema Extension Error = 8224

I bumped into this issue today on a customer site. The Schema Extension failed with error code = 8224, which you can view it from the C:\ExtAdSch.log

Here are the steps I checked:

1. Schema Extension needs to be performed all the DC holding all the FSMO roles. Open Command Prompt and enter netdom /query fsmo
2. The user account is part of the Schema Admins group
3. Check the AD Replication between the domain controller using repadmin command. It showed replication error, and this is the reason causing the Schema Extension failure.

Thanks for reading =)