freebsd stable - May 2006 - Can't boot: Guessed BIOS device 0xffffffff not found by probes....

Hello,

[I previously posted this to questions@, maybe stable@ is better suited]

I have been running along just fine till a cvsup this morning (05/30). 
Last successful cvsup was May 20th.  After cvsup today, and a 
"build-world" I see something _similar_ to below when trying to boot.

---------------------------
Can't work out which disk we are booting from.
Guessed BIOS device 0xffffffff not found by probes defaulting to disk0:
panic: free: guard1 fail @ 0x517c4 from [line folded for mail]
/usr/src/sys/boot/i386/loader/../../common/module.c:957
---------------------------

(I say similar, becuase the above text is actually copied from another
web post.  But mine is similar.  If *my* text is needed I can reproduce
the issue to obtain it.)

I did a google or two and found nothing of use.  Maybe I am using the 
wrong keywords.

If I bring the machine up in Safe Mode or with ACPI Disabled everything 
is fine (I am writting this from the machine in question).  Nothing else 
has changed other than a cvsup and build-world (meaning no hardware/BIOS 
changes).

Anything I can provide to help diagnose this?

I am running FreeBSD 6.1-STABLE #0: Wed May 31 12:05:21 CDT 2006 on a 
Dell Inspiron 5100.  I have cvsupped back to 05-15-2006, which is before 
my last known good cvsup and things still fail.  So now I am wondering 
if some hardware has failed.

Any ideas?

-- 
Regards,
Eric