ERROR_UNEXPECTED_MM_EXTEND_ERR - 558 (0x22E)
If an MM error is returned which is not defined in the standard FsRtl filter, it is converted to one of the following errors which is guaranteed to be in the filter. In this case information is lost, however, the filter correctly handles the exception.
Updated: Feb 21, 2026
Technical Meaning
The error code ERROR_UNEXPECTED_MM_EXTEND_ERR (558, 0x22E) is encountered when a memory management extension error occurs that is not defined in the standard FsRtl filter. This error is then converted to one of the guaranteed errors within the filter.
Error Details
When an unexpected memory management error is detected during file system operations, it may not be directly handled by the standard FsRtl (File System Routines Library) filters. To ensure consistent behavior across different scenarios, such unhandled errors are mapped to a predefined set of errors that are guaranteed to be recognized and processed correctly by the filter.
Usage Context
This error typically arises in situations where custom memory management extensions interact with the file system routines but fail in an unexpected manner. The conversion to a standard error code ensures that the system can continue processing without interruption, albeit at the cost of potential information loss regarding the specific nature of the original error.
Developer Interpretation
Developers should be aware that this error indicates a failure within memory management extensions during file operations. While the exact cause may not be immediately clear due to the conversion process, it is important to review the context in which the operation was performed and ensure that all custom memory management routines are correctly implemented.
Related Errors
ERROR_INVALID_PARAMETER(1258, 0x4E6)ERROR_NOT_ENOUGH_MEMORY(1222, 0x4C6)ERROR_OUTOFMEMORY(1403, 0x57B)
FAQ
Q: What does ERROR_UNEXPECTED_MM_EXTEND_ERR mean?
A: It indicates an unexpected memory management error that is not defined in the standard FsRtl filter and is converted to a guaranteed error.
Q: How can I handle this error in my application?
A: Review the context of the operation, validate parameters, and ensure all custom memory management routines are correctly implemented.
Summary
ERROR_UNEXPECTED_MM_EXTEND_ERR (558, 0x22E) is a generic error code that indicates an unexpected memory management extension error during file system operations. It ensures consistent handling by converting the error to a predefined standard error, but may result in loss of specific information about the original error.