Kernel panic while playing CoD4 on new MP

I decided to kill a little time and cranked up CoD4. I've played this game for years on my MP1,1 (x1900 and later 4870 GPU) without problems. After a couple of minutes in a match, I thought I saw a horizontal line on the screen for a split second. About a minute later, the game and machine froze up. After a hard shutdown and reboot, I found a kernel panic log. What worries me is that I think I saw a similar line "flash" previously but I was not sure at the time I actually saw it (it's very quick).

2010 Hexacore with 5870, 8GB RAM.

Anyone else experiencing anything like this under intense graphics activity?

Top of panic log:

Interval Since Last Panic Report: 135473 sec
Panics Since Last Report: 1
Anonymous UUID: 23CCB264-B5E0-4091-8907-576AAF73FD7D

Fri Sep 3 17:20:33 2010
panic(cpu 10 caller 0xffffff800020931a): "thread_invoke: preemption_level -1, possible cause: unlocking an unlocked mutex or spinlock"@/SourceCache/xnu/xnu-1504.7.60/osfmk/kern/sched_prim.c:1476
Backtrace (CPU 10), Frame : Return Address
0xffffff80b2443d70 : 0xffffff8000204b99
0xffffff80b2443e70 : 0xffffff800020931a
0xffffff80b2443ef0 : 0xffffff80002098fe
0xffffff80b2443f60 : 0xffffff8000284d13
0xffffff80b2443fa0 : 0xffffff80002c63c7

BSD process name corresponding to current thread: kernel_task

Mac OS version:
10F2521

Kernel version:
Darwin Kernel Version 10.4.2: Tue Jul 27 21:17:17 PDT 2010; root:xnu-1504.7.60~1/RELEASE_X86_64
System model name: MacPro5,1 (Mac-F221BEC8)