Similar symptoms:

Walk away from LW 4.10.5 left running and find windows XP sp2 completely shut down. Upon restart, active desktop error is displayed.
No problems with next earlier LW version - 4.9?
No active desktop items.
I do run starstonesoftware.com/eots "eye of the storm" screensaver. Does that qualify as an active desktop item?
XP firewall off. No difference if left on.
No other firewalls.
I've beaten power settings to death.
No other crashing.
As long as I occupy myself with other applications, LW and XP continue to run. Once left to their own devices, the shutdown inevitably occurs.
What is timing me out?
ISP issue?
I relinquished some more free will to microsoft and finally installed sp2 at about the same time as LW 4.10.5. SP2 issue?

Too many questions? For shame....

LW 4.10.5
java 1.5.0_04
nom 56K dialup - 44K is normal connection
XP sp2 - last full update 21 Feb 2006