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ERROR_DOMAIN_CONTROLLER_EXISTS
A domain controller with that name is already present.
ERROR_DOMAIN_CONTROLLER_EXISTS is Win32 error 1250 (0x4E2). It blocks an operation that would create, promote, or register a domain controller using an identity already known to Active Directory. The existing identity may represent a healthy controller, an interrupted promotion, or stale metadata from a controller that was removed incorrectly.
Do not treat the name collision as a simple computer rename
A domain controller has directory objects, service principal names, DNS records, replication metadata, and a machine account. Deleting one visible computer object or changing the local host name does not necessarily remove all of that identity. Before modifying anything, determine whether the existing controller is live and authoritative.
Evidence to capture
- the proposed NetBIOS and DNS host names
- domain and forest names, target site, and promotion method
- existing server and NTDS Settings objects with the same identity
- DNS host, SRV, and CNAME records associated with the controller
- replication state and the last successful contact with the existing machine
Diagnostic sequence
Use Active Directory Sites and Services and directory queries to locate every object representing the name. Verify whether the existing domain controller responds, advertises services, and participates in replication. If it is offline, establish whether it is temporarily unavailable or permanently decommissioned.
For a failed previous promotion, review Directory Service, DNS Server, and deployment logs before cleanup. Stale metadata removal is an administrative recovery procedure, not a routine installer action. Replication must propagate cleanup before the name is reused, otherwise different controllers can hold inconsistent views.
Recovery options
If the controller is healthy, choose a unique name for the new server. If the old controller was forcibly removed, complete documented metadata cleanup, remove stale DNS records only after verification, and wait for directory replication. Then repeat promotion with a fresh deployment record. Never automate destructive cleanup solely on error 1250.
Related codes
ERROR_DOMAIN_EXISTS concerns a domain identity, not a controller within it. ERROR_NO_SUCH_DOMAIN indicates that a domain could not be found. Error 1250 specifically says the requested domain-controller name is already registered.
Example
A virtual machine is rebuilt with the name of a domain controller that failed months earlier. Promotion returns 1250 because the NTDS Settings object and DNS aliases remain. Administrators verify that the old controller will never return, perform metadata cleanup, allow replication to converge, and only then reuse the name.
References
- Microsoft: System Error Codes (1000–1299)
- Microsoft: Install Active Directory Domain Services
- Microsoft: Clean Up AD DS Server Metadata
- Microsoft: Security Identifiers
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