What does Windows error code 558 (ERROR_UNEXPECTED_MM_EXTEND_ERR) mean?

ERROR_UNEXPECTED_MM_EXTEND_ERR

FsRtl converted an unrecognized memory-manager extend error

ERROR_UNEXPECTED_MM_EXTEND_ERR is a fallback translation boundary. An error returned by the memory manager was not represented in the standard FsRtl filter, so Windows converted it to a guaranteed filter-visible result. This value identifies the extend side of that fallback path; it does not preserve the original detailed memory-manager status.

Do not over-interpret the suffix

The word EXTEND tells you which fallback result was selected, but it does not prove that the volume was full, a mapped file was concurrently truncated, or a filesystem filter caused the failure. Those are hypotheses that require lower-level evidence.

What to collect

• Record the exact object, file or section, old and requested new size, filesystem and volume identity, and the API that first returned the translated error.
• If the failure is reproducible, capture the original kernel/filesystem status before the FsRtl translation, because that value carries the cause that this Win32 result has lost.
• Correlate free-space, storage, filesystem and filter events only for the same attempt; later recovery errors should remain separate.

Recovery boundary

Fix the condition identified by the original status and recreate or reopen the affected object as required by its API contract. Do not keep using an object whose extend operation did not complete, and do not treat increasing free space as a universal remedy without evidence of a capacity failure.

References

• Microsoft: System Error Codes 500–999
• Microsoft: Retrieving the last-error code