Vista is hanging. Event ID 12338 is undocumented. MVP Help may be needed.

My Vista laptop (Dell Latitude D630) hangs between one and two times every
day. This almost never happens while I am using the system, only when I
have left it for a while. The symptom is that the clock has stopped at some
past time, and the disk activity light is off and stays off. The mouse can
be moved, and if I click, I get the spinning disk cursor (which can still be
moved!), but nothing else happens. There are no blue screens, and almost
nothing of note in the error log, with one exception, which appears about
one in four times that it hangs up:

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Log Name: Application
Source: VSS
Date: 2/4/2008 7:12:12 PM
Event ID: 12338
Task Category: None
Level: Error
Keywords: Classic
User: N/A
Computer: FEJNoteVista
Description:
Volume Shadow Copy Error: VSS spent more than 120 seconds trying to open and
flush all the volumes in the shadow- copy set. This caused volume
\\?\Volume{be9166c2-7bd3-11dc-ad5a-806e6f6e6963}\ to timeout waiting for the
hold-writes phase of shadow-copy creation. Trying again when disk activity
is lower may solve this problem.

Operation:
Executing Asynchronous Operation

Context:
Current State: flush-and-hold writes
Volume Name: \\?\Volume{be9166c2-7bd3-11dc-ad5a-806e6f6e6963}\

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The above message appears 2 minutes AFTER the clock stops. For that reason,
thing it's possible that VSS is going haywire, and causing the problem.
It's also possibly that it represents a symptom rather than the cause (i.e.
something is siezing control over my hard drive, and so that it can't flush
buffers, and it gets one last line written to the system log before
everything hangs up.)

THERE IS NO INDICATION ON THE WEB THAT Event ID 12338 HAS EVER BEEN REPORTED
ON ANYONE ELSE'S PC!

I've done memory & other diagnostics. More importantly, I've swapped my
hard drive into another PC shell with the identical configuration. The
problem stays with the drive, so unless it's the disk itself (and why would
that only hang overnight or in other idle periods?) then it's something in
the software.

Other things which have failed to fix the problem:

* Uninstalling X1 indexer
* De-scheduling SyncBack SE backups (it was hanging for sure, when trying to
run a backup at 1:00 AM each night)
* Turning off all power savings on my hard drive
* Cold booting the system and leaving it at the login prompt overnight
(system was frozen the next morning.)
* Turning off UAC
* Turning on UAC

MOST (but not all) of the hangups occur at "round" times, such as 1:00 AM or
4:00 AM. I get the feeling that there is something flakey going on which is
causing the hard disk to hang up, and that when one or another scheduled
event comes along to access the disk, whereupon the entire OS goes into
shock.

The one other flakey thing that I notice on this PC is that even after I
close Outlook, it continues to run in the background. However, I think that
may be due to some utility like Kaspersky keeping a MAPI session open.