ERROR_DS_FLAT_NAME_EXISTS_IN_FOREST 0x800721BB

Error code 8635 · HRESULT 0x800721BB

WINDOWS

The flat name of the trusted domain already exists in the forest.

Windows troubleshooting diagram: Device Manager warning and a system file scan
Windows errors: check drivers, system files and Event Viewer, in that order.

What it means

ERROR_DS_FLAT_NAME_EXISTS_IN_FOREST is a Windows error code (system error 8635, returned as HRESULT 0x800721BB) reported by Windows. Its official message is: “The flat name of the trusted domain already exists in the forest.”

How to fix ERROR_DS_FLAT_NAME_EXISTS_IN_FOREST

  1. Run the affected program as administrator (right-click → Run as administrator)
  2. Check permissions on the target resource: Properties → Security → your account
  3. Check Event Viewer → Windows Logs → Security for the matching audit entry

Related errors

ERROR_DS_DOMAIN_NAME_EXISTS_IN_FORESTERROR_DS_DRA_MISSING_KRBTGT_SECRETERROR_DS_OID_MAPPED_GROUP_CANT_HAVE_MEMBERSERROR_DS_MAPI_ID_NOT_AVAILABLEERROR_INVALID_USER_PRINCIPAL_NAMEERROR_DS_OID_NOT_FOUNDERROR_DS_RESERVED_MAPI_ID

Source: Microsoft WinError.h

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