What does Windows error code 561 (ERROR_INVALID_LDT_SIZE) mean?

ERROR_INVALID_LDT_SIZE

An attempt was made to grow an LDT by setting its size, or the size was not an even number of selectors.

ERROR_INVALID_LDT_SIZE is Windows system result 561 (0x00000231). Microsoft defines it as “An attempt was made to grow an LDT by setting its size, or the size was not an even number of selectors.”

How to classify the result

This result represents an x86 Local Descriptor Table size validation failure. The correct interpretation depends on the low-level x86 or WOW compatibility operation that supplied the LDT byte count and selector range.

Where it can appear

• This result can appear in legacy x86 execution support.
• This result can appear in a debugger or compatibility component inspecting descriptor-table entries.
• It can appear in low-level code translating a native LDT status into Win32.

Typical causes

• the requested size is not a multiple of the selector-entry size.
• the operation attempts to grow the table through a size-setting path that does not permit growth.
• a byte count was confused with an entry count.
• 32-bit layout assumptions were used on an unsupported architecture.
• integer truncation produced a misaligned final size.

Useful evidence

• Record processor architecture and WOW state.
• Record requested LDT size in bytes and entries.
• Record selector-entry structure size.
• Record calling system service or compatibility component.
• Record native status before Win32 mapping.

Recovery and retry

Correct the count and alignment, or remove the unsupported attempt to grow the LDT through the size-setting request.

Do not retry the same size. Retry only after recalculating the request from validated entry boundaries and confirming the operation is supported on the current architecture.

Difference from related results

ERROR_INVALID_LDT_OFFSET concerns where the update starts; ERROR_INVALID_LDT_DESCRIPTOR concerns descriptor contents. It is about the total requested extent.

Example

A 32-bit compatibility tool multiplies a selector count by the wrong packed structure size and submits an odd extent. Logging the count, byte size, and sizeof result makes the alignment error visible before any descriptor is changed.

Developer and administrator guidance

Keep LDT manipulation isolated behind architecture checks. Modern applications should not introduce new dependencies on x86 descriptor tables; compatibility tooling should validate every count before entering the system service.

References

• Microsoft: System Error Codes 500–999
• Microsoft Open Specifications: Win32 error values
• Microsoft: LDT_ENTRY
• Microsoft: GetThreadSelectorEntry