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:
- Schema Extension needs to be performed all the DC holding all the FSMO roles. Open Command Prompt and enter netdom /query fsmo
- The user account is part of the Schema Admins group
- 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 =)