"CPU0: local APIC error 0x40"

[Edward Tomasz Napierała]

Some machines, including ThinkPad T61, emit the following error message
early during boot:

CPU0: local APIC error 0x40

The message itself doesn't seem to be much of a problem.  However,
every once in a while booting hangs just before that line.  I've tracked
that down to call to AcpiHwWritePort() at
sys/contrib/dev/acpica/components/hardware/hwacpi.c:117:

    switch (Mode)
    {
    case ACPI_SYS_MODE_ACPI:

        /* BIOS should have disabled ALL fixed and GP events */

        Status = AcpiHwWritePort (AcpiGbl_FADT.SmiCommand,
                        (UINT32) AcpiGbl_FADT.AcpiEnable, 8);

Any idea what might be going on?