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ERROR_EXTERNAL_SYSKEY_NOT_SUPPORTED
The configured Syskey mode is no longer supported
ERROR_EXTERNAL_SYSKEY_NOT_SUPPORTED means Windows detected a legacy configuration in which the system key was protected by an external startup mechanism that current Windows versions no longer accept. This is a configuration-compatibility failure, not an ordinary password or removable-media read error.
Where it can appear
- During startup, recovery, upgrade, or servicing of an installation that was configured with an older Syskey mode.
- When restoring a system image or registry hive created on an older Windows release.
- When migration software preserves unsupported security metadata even though the operating-system binaries have been upgraded.
Diagnosis
Confirm the Windows version, the origin of the installation or image, and whether the system was upgraded from a much older release. Preserve upgrade and setup logs. Do not assume that the external key file is merely missing: the key-protection mode itself may be rejected.
Recovery approach
Use Microsoft-supported recovery or migration guidance for the affected release. Avoid editing SAM or SYSTEM hives by hand unless working from a verified offline backup and a documented procedure; an incorrect change can make the installation unbootable or invalidate account data.
Developer and support notes
Software that inventories or migrates Windows installations should report the legacy protection state explicitly and stop before destructive conversion. The error should be escalated as a platform-compatibility issue rather than retried.
References
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