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ERROR_CANTOPEN
Windows could not open the requested registry key
Opening a registry key resolves a subkey beneath an existing HKEY and requests a specific access mask. ERROR_CANTOPEN identifies failure at that open stage; it does not mean that a later value read or write failed. The distinction matters when a caller collapses all registry errors into a generic configuration failure.
Record the parent handle, subkey path, view flags, and requested access. Check whether the key exists in the registry view used by the process and whether the caller requests more rights than it needs. On 64-bit Windows, registry redirection can make a key appear in a different view for 32-bit and 64-bit processes. Do not create the key automatically unless the application owns that configuration namespace; a missing system or service key can be evidence of incomplete installation or deleted configuration.
What to inspect
- Log the parent HKEY, relative subkey, requested rights, and WOW64 view flags.
- Test the same path with the minimal access needed by the operation.
- Do not auto-create system-owned keys to hide a failed open.
References
- Microsoft: RegOpenKeyExW
- Microsoft: Structure of the Registry
- Microsoft: Database of Installed Services
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