URGENT -- AP #1 (PHY #1) failed -- what does this mean?

[Chad Leigh -- Shire.Net LLC]

Hi

Sorry for the URGENT line.  I have a critical server running 5.4- 
RELEASE-p1.  It is a dual AMD MP 2800+ (Gigabyte board) with 4GB RAM  
and an Adaptec 2100S raid controller.

Running (obviously) an SMP kernel.  I recompiled the kernel this  
afternoon and changed one line --  the

options  HZ  line from HZ=1100 to HZ=400 as a test of PHP  
performance.  That was the only thing changed  (the machine had been  
up since I installed 5.4 on it June 1).  I built and installed the  
kernel and tonight I rebooted the machine.

Now when it boots it comes up and

real memory = 3758030848 (3583 MB)
avail memory = 3678240768 (3507 MB)
ACPI APIC Table: <GBT     AWRDACPI>
AP #1 (PHY# 1) failed!
panic y/n? [y]


What does this mean (and what do I do about it)?

I am off to Google but as I am in a real tight spot I thought I would  
ask for some help asap before I go and try and figure this out.

Thanks
Chad