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ERROR_DS_INSTALL_SCHEMA_MISMATCH
Promotion found a schema level that the candidate DC cannot use
Domain controller deployment validates the forest schema before installing a replica. Current deployment tooling discovers the Schema Master and checks the schema objectVersion to determine whether preparation or extension is required. A mismatch at this stage means the source forest and the directory-service binaries on the candidate are not in a supported schema relationship.
Read the schema version from the Schema naming context and compare it with the expected version for the Windows Server build being promoted. Check ADPrep and deployment logs to see whether schema preparation was required, attempted, or failed. Do not repair this by changing objectVersion numerically: the version represents a set of schema changes, and the corresponding class and attribute definitions must actually exist and replicate.
What to inspect
- Read the schema objectVersion from the forest rather than relying on a server label.
- Review ADPrep and Dcpromo logs for the first schema-preparation failure.
- Verify schema changes replicated from the Schema Master before retrying promotion.
References
- Microsoft: AD DS deployment and prerequisite checks
- Microsoft: find the Active Directory schema version
- Microsoft: Windows Server AD schema updates
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