Debian :: Squeeze Broken After Updates Applied

I am running Squeeze AMD64 and install updates every couple of days. I installed the latest batch yesterday and got a "restart system" message, so rebooted. The usual messages scrolled past for a while, then the screen went blank, and that was it. I tried a couple of times with same result. I booted into maintenance mode to try to find the cause of the problem. Looking at /var/log/messages there is some strange activity going on. Unfortunately I can't easily paste the relevant portion of the file into this posting as the network isn't working (I am posting this from a laptop), but roughly what I am seeing is this:

PGD <some stuff>
CPU 0
Modules linked in: <long list of modules>
Pid, 1841, comm: Xorg Not Tainted <some stuff>
<about 20 lines of assorted values>
--[end trace <long hex number>]

and this repeats several times (presumably stopping when I hit the reset button). Sometimes it's CPU 0 and sometimes CPU 1, it mostly involves Xorg in Pid line, and apart from the first instance mostly reports Xorg Tainted.

I could just reinstall but would rather repair as it would be both quicker and more instructive.