What does Windows error code 791 (ERROR_BAD_MCFG_TABLE) mean?

 
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ERROR_LOST_WRITEBEHIND_DATA_LOCAL_DISK_ERROR ERROR_DISK_REPAIR_REDIRECTED

ERROR_BAD_MCFG_TABLE

device resources conflict with the firmware mcfg table.

ERROR_BAD_MCFG_TABLE indicates this condition: The ACPI MCFG table describes PCI Express enhanced configuration-space regions. Windows detected that resources required by a device overlap or disagree with those firmware declarations, making direct configuration-space access unsafe.

Where the result appears

  • PCI Express device enumeration during boot.
  • chipset or bus-driver initialization.
  • firmware updates that alter PCIe resource windows.
  • virtual machines or unusual platforms presenting an invalid ACPI layout.

What to collect

  • the MCFG entries, base addresses, segment groups, and bus ranges.
  • the conflicting device resources from Device Manager or SetupAPI logs.
  • system model, BIOS/UEFI revision, and chipset driver version.
  • whether the problem appeared after firmware, hypervisor, or hardware changes.

Handling and recovery

Update the system firmware and chipset components from the platform vendor. Restore default firmware settings, remove recent PCIe hardware to isolate the conflict, and provide ACPI tables to the vendor if the platform still publishes an invalid map. Application retries cannot correct firmware resource descriptors.

Common misinterpretation

This is not a malformed application configuration file. MCFG is an ACPI firmware table used for PCI Express configuration access.

References


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