About once every other day, or more depending on the amount I work during the day(s), Sonar X3 crashes to a BSOD.  I get a constant loop of the last millisecond or so of wherever I was on playback.
 
Here's what I know of when it happens.

1. It always happens on playback.
2. It's always during a mix session that's 1/2 or more done (meaning heavy plugin usage, session drummer often in use, a lot of frozen tracks, etc).
3. It's never happened when I'm tracking in X1.  I track on X1 because I can comp/edit WAY faster in track layers, but that's another topic.
4. It's happened in every version of X3 that I can remember.  X3a-e.

 
I use X1e 32-bit on a 64-bit W7 PC.  I use 32-bit due to lack of time to get certain plugins set up and ported to 64-bit.  To read why please see the footnote below.  I have 16Gb RAM, but obviously Sonar can't use it with my 32-bit install.  I use a Lynx Aurora 16 with a Lynx AES-16.  I track and mix at 48K.
 
If anyone has any idea how to help me track down the reason for these crashes please let me know.  I would appreciate it very much so, and so would my PC :)

** For the past few months I just don't have much time to be not working when I'm at my PC, so I'm sticking with 32-bit for the foreseeable future.  I have a feeling it'll take some time for me to get things set up properly for 64-bit.  I know things don't always transition easily 100%, so I need to allow time for some troubleshooting.

The looping audio upon crash is the last bit of audio that was in the buffer (looping).
 
BSOD is usually indicative of a hardware or driver issue.
In a modern machine, the most likely culprit to fail is a stick of DDR3.
Thus, I'd test your RAM to be sure all is ok.
I'd follow that up by running a stress-test to make sure the core hardware (CPU, motherboard, RAM) are ok.
If the machine passes those tests without a problem, you can rule out the machine itself.
 
Since the issue doesn't happen when tracking (not using much RAM), I have a suspicion that you may be "RAM starving" Sonar when mixing.  With a full mix (especially if you're using any virtual instruments), it's really easy to blow thru 4GB of RAM (which is the limit for any 32Bit application).
 
As a test:
Install the 64Bit version of Sonar (if not already installed).
Open your project in the 32Bit version of Sonar, use the 32Bit plugins mentioned above), then freeze the results and save under a different file name.
Now, open this new file using the 64Bit version of Sonar.
If you can do this and continue without BSOD, you've found the culprit (RAM starved application).
If that's the case, using a 64Bit DAW application is the only solution.

Thank you!!! How do you stress test a machine, other than doing the 64bit test you described later in the reply?

fooman
Thank you!!! How do you stress test a machine, other than doing the 64bit test you described later in the reply?

You can use Prime95 to stress-test your core hardware.
It puts the CPU under 100% load (sustained).
Note, keep on eye on CPU temps if you run Prime95.

If you are getting a BSOD error, you need to tell us the stop code.  That will give us a much better idea of what's going on.  Have a look for "Nirsoft BlueScreenView" on Google.  Make sure to grab the 64-bit version.  It will give you more information about the crash and what caused it.
 
As Jim has already said, applications can't cause blue-screens.  It is caused by bad hardware or something happening in Kernel mode (bad drivers).

Silicon Audio
If you are getting a BSOD error, you need to tell us the stop code.  That will give us a much better idea of what's going on.  Have a look for "Nirsoft BlueScreenView" on Google.  Make sure to grab the 64-bit version.  It will give you more information about the crash and what caused it.
 
As Jim has already said, applications can't cause blue-screens.  It is caused by bad hardware or something happening in Kernel mode (bad drivers).

 
+1.
 
I had an issue like this yesterday, from here I was able to locate the issue was related to mcupdate.dll. From that I gathered that Windows Media centre was trying to update itself and somehow causing the crash. As I don't use Media Centre on my DAW I uninstalled it.... Fingers crossed no more issues.
 
Your issue will be driver related or hardware related. You might want to post the BlueScreenView report here if you can't work it out. Generally the suspect exe/dll's/.sys are at the top of the list. Still often requires some hunches/guesswork though. The windows event viewer often helps as well...

Will just about guarantee it is due to your audio interface. I use a Pod X3 and that causes crashes more than Sonar.

Had the same issue.  Pulled the CPU, fan and heat-sink out of my ASUS CM1630 case and found a lot of crud on the heat-sink.  Managed to bend some pins on the CPU when attempting to re-insert it. Consequently I ended up buying a new ASUS M11 series.  I've had no recurrence of BSOD.    After seeing the buildup of dust and grime on the original CPU's heat-sink,  I can't help but believe that it was overheating and causing the BSOD.  My rather uninformed guess is that Sonar may overburden the CPU when it is cranking out its stuff. If enough heat energy is not dissipated because of a dirty heat-sink the conditions are then possibly ripe for a BSOD attack.  I had similar problems with another computer a few years back  that was unrelated to Sonar.  Cleaning the guts and the heat-sink fixed it!
 
I'll remain curious as to what you find is at the root of your BSOD atacks.
 

I haven't been able to do MUCH in terms of troubleshooting this, but I did take a look at the memory used on one culprit project.  3.44Gb of memory used after a fresh restart.  I'm assuming that after not restarting my PC for over a week and using it often the memory usage might gradually creep up to the 4GB limit with the 32-bit app like my Sonar install.
 
I also just cleaned my PC's guts this past weekend.  Was much overdue.
 
I am almost certain it's not my Lynx drivers.  Although I haven't updated the drivers since Sonar X1 or so!  Who knows, it's on my list of potentials I guess :)

Well if you haven't updated your drivers for a while that's a red flag. Please run windows update several times as well..