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ERROR_FLT_INSTANCE_ALTITUDE_COLLISION
Two instances cannot share one position in a volume stack
ERROR_FLT_INSTANCE_ALTITUDE_COLLISION means that an instance is already attached at the requested altitude on the target volume. In Filter Manager, altitude is a decimal string that determines an instance's relative position in the minifilter stack. A higher altitude is farther from the base filesystem, and only one instance can occupy a given altitude on the same volume.
This is not the same as a driver load-order problem or an instance-name conflict. It specifically identifies a stack-position collision. The collision can arise from an explicit debug attachment, a duplicate instance definition, or a stale assumption about what is already attached to the volume.
What to check
- Inspect the active stack with
fltmc instancesand compare the actual filter, volume, instance name, and altitude before attempting another attach. - Review the minifilter INF instance definitions and the assigned altitude. Do not invent a new production altitude merely to bypass a collision; altitude allocation is tied to filter function and load-order groups.
- Distinguish this status from
ERROR_FLT_INSTANCE_NAME_COLLISION. The former is about the stack position on one volume; the latter is about the instance identity. - Remember that
FltAttachVolumeAtAltitudeis documented for debugging. Correct automatic attachment configuration rather than relying on it in a retail driver.
References
- Microsoft: FltAttachVolumeAtAltitude
- Microsoft: load order groups and altitude allocation
- OSR: deterministic layering and filter instances
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