HRESULT 0x801F0012 (ERROR_FLT_INSTANCE_NAME

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A minifilter instance with the requested name already exists on the volume.

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ERROR_FLT_INSTANCE_ALTITUDE_COLLISION	ERROR_FLT_FILTER_NOT_FOUND

ERROR_FLT_INSTANCE_NAME_COLLISION

The instance identity is already in use

ERROR_FLT_INSTANCE_NAME_COLLISION indicates that the requested instance name is already attached on the target volume. The name can be supplied directly to an attach call or selected from the driver's configured default instance. It identifies an instance, not a file-system path and not an altitude by itself.

A filter can legitimately have multiple instances, so a name collision does not necessarily mean the whole filter is duplicated. It means the requested identity would not be unique. In the ordinary attach API, instance names are expected to be unique across the system, while the corresponding instance attributes such as altitude can be read from the driver's configuration.

What to check

Use fltmc instances to find the existing attachment and compare its filter, volume, altitude, and instance name.
Verify the service's configured default instance and every explicit InstanceName used by an administrative or test tool.
Do not change the name blindly if the existing instance is the intended one. Reuse its handle or inspect its state instead of creating a second logical copy.
Differentiate this error from ERROR_FLT_INSTANCE_ALTITUDE_COLLISION: names identify instances, whereas altitude controls their stack position.

References

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