Mac Pro freezes frequently after "NVChannel" error in system.log

Question

Hi,
Can anybody here with a 2008 Mac Pro run the Folding @ Home client without hard crashing the Mac?
I have a 2008-model Mac Pro, with the nVidia GeForce 8800 GT, which freezes frequently. As detailed in an earlier post[1], the graphics driver sees to be implicated, as just before the freezes, messages like this appear in the system log:
kernel kern 3/30/08 7:53:52 PM Debug NVChannel(GL): Graphics channel exception! status = 0xffff info32 = 0x6 = Fifo: Parse Error
kernel kern 3/30/08 7:53:52 PM Debug 0000000b
If you google for "NVChannel freeze" then you will find many many Mac owners whose machines freeze with similar symptoms. Apple recently released the "Leopard Graphics Update" which fixes such problems for some users, but not others.
In my 2008 Mac Pro's case, I have found a way to trigger the freeze 100% of the time: install the freeware Folding@Home client[2], and run the demo in the Applications folder. Just opening this app causes those messages to appear in the log, and then the Mac freezes.
I work for a software company which writes Mac software, so now that I have found a reliable way to reproduce this issue, I will be filing a bug report through Apple's bug system. But for my own sanity, I would like to collect more info, if possible.
If you have a 2008 Mac Pro and want to be cool, try running the Folding @ Home client app (link below) and post in this thread:
a.) whether or not your Mac froze
b.) what video card you have
c.) how much RAM you have
Thanks!
[1]: http://discussions.apple.com/thread.jspa?messageID=6920946&#6920946
[2]: http://folding.stanford.edu/English/Download

Answer 1

Yup… this is a memory fault and you should firstly try reseating the RAM and memory Risers (even change the slots they are in - depending on your configuration of course). The can often remove these issues.
Failing that, I would contact the RAM vendor and discuss it with them. Depending on how they sell things it might be simpler to send a kit, as in two DIMMs, back for replacement rather than a single DIMM that is part of a kit. Also, unless they specifically match your original DIMMs then you'd be better of returning both.