Error Message: ACPI BIOS Is Attempting to Create an Illegal Memory OpRegion

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This article was previously published under Q330054

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SYMPTOMS

You may receive the following event message in the event log when you open the Event Viewer:

Source: ACPI
Category: None
Type: Error
Event ID: 12
User: N/A
Computer: ComputerName
Description: AMLI: ACPI BIOS is attempting to create an illegal memory OpRegion, starting at address 0x400, with a length of 0x100. This region lies in the Operating system's protected memory address range (0xXXXX - 0xYYYY). This could lead to system instability. Please contact your system vendor for technical assistance.

For more information, see Help and Support Center at:
http://support.microsoft.com

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CAUSE

This behavior occurs because the basic input/output system (BIOS) provides information about all the memory present in the computer to the Windows XP operating system and tells Windows which memory address ranges are valid for the operating system to use. When the Advanced Configuration and Power Interface (ACPI) BIOS creates memory operation regions, Windows checks the category of memory in which they are being created. If the ACPI BIOS creates the memory operation region within a memory range that the BIOS earlier said that the operating system can use, Windows logs the event message to the system event log.

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