Crash (forced restart) after sleep

[bautz]

iBook (dual usb 600, 10.3.9) exhibits since Sunday an odd behaviour:

When waking it up from sleep, a gray layer appears over the complete screen, with a multilingual warning that I must restart. Nothing else but that will do, password-entering or any other action is disabled.

I tried the first lines of defense:
• repaired permissions with DiskUtil and Applejack. Results: some permissions come up again and again as wrong, and even though they report as being repaired, next round they show up as faulty again
• rebuilt directory with DiskWarrior
• Applejack also reported itunes 7.1.1, which I downloaded the day the trouble began, as containing "malformed" elements, which could not be repaired. Possibly unrelated though, but I deleted itunes completely, though with no changes of the problem
• restart from CD, no repairs necessary per DiskUtil

Does anyone have an idea what the heck this is, and what I can do to remedy the situation?

TIA,

-bautz.