DifferentByDesign,
 
Is this a USB or a FireWire device? You might post some of your system specs in your forum signature to make helping you easier.
 
So, what you probably want to do is make some tweaks to some settings and re-run the latency monitor to see if you have removed the issue.
 
There are a few likely culprits...

• USB Selective Suspend
• Video Driver
• Battery if it's a laptop

 
 
You want to turn off USB Selective Suspend...
 
This link describes it...
http://msdn.microsoft.com/en-us/library/windows/hardware/ff540144%28v=vs.85%29.aspx
 
This link talks about how to disable it...
http://www.sevenforums.com/tutorials/147369-usb-selective-suspend-turn-off.html
 
Since this is the easiest thing to try, give it a go and report back.
 
Next suggestion will be to go into device manager and disable acpi compliant battery if it's a laptop (be sure you're plugged in first) and maybe the video driver.
 
 

@Gswitz
 
Yes it is a Firewire Interface Specifically a Focusrite Saffire Pro 40 connected to a PCI Firewire /USB combo card. CPU load on the machine while playing back multitrack ( approx 20) Audio is only a few % and Memory use is negligible. This isnt a resource issue as I have played this song on my older slower and dumber machine with no issues many times.
PC Spec as follows ( I5 3.4ghz Quad core processor, 120gb SSD, 8gb of RAM and Windows 7 64 bit OS. Interface is a Focusrite Saffire Pro 40 Firewire. Running Sonar 8.5 Studio, X2 and X3 Producer)
USB Selective suspend disabling made no difference.

good to know it's firewire. USB Selective Suspend wouldn't matter in that case. Sorry I had to ask. I see you posted it initially.
 
Firewire cards can be troublesome. Sometimes folks who have the ability will try a different card. I don't know if this is a possibility for you.
 
Something you could try is disabling the firewire card in the Device Manager and running the Latency Monitor to see if your DPC Latency issue resolves.
 
Right now we're just trouble shooting it. Obviously you can't live without Firewire, but perhaps you could get a new firewire pcicia card that ONLY does firewire. Firewire can be funny on Windows machines in part b/c of the drivers and in part b/c of the amount of current Firewire supplies to devices.
 
I5 processor sounds like a laptop, but I'm not sure. Laptop or desktop? Can you open the case and put in your own Firewire card?
 
I have an old laptop that has a firewire port that NEVER worked properly for audio interfaces. It worked for capturing video from my DV Camera, but it was useless with three different firewire interfaces including my RME. The RME also has USB which works fine on the same computer. Now, my laptop had a cheapo firewire port. Yours is probably much better. I'm just trying to rule it out.
 
To some degree, you just want to keep restarting the latency monitor as you run around disabling things until you DON'T get problems reported by the DPC monitor. Then re-enable everything one thing at a time to see what you need to disable for audio work.
 
It may be something small. It'll just take some tedious trouble shooting in Device manager. Don't uninstall things. Just try disabling them. And, btw, even if you do uninstall from device manager, you PC should just reinstall them on reboot.

Its a desktop not a laptop.
Swapping out the card is not an option without buying extra cards
Latency monitor runs fine till you fire up Sonar then sometime in the next minute it craps out.
It seems (SEEMS) that it might be being caused by a wireless LAN card which i also cant live without.
Just testing this theory out now

I also have another rather bizarre issue in that whenever Sonar is the active window a high pitched buzzing sound can be heard (ie: outputted from) the interface which is independent of and level settings or mutings. It is not high in volume but you really notice it when you switch to another window!
I dont know if its related or not but i suspect it is.

Hi pitched buzzing may be related to the power being sent through the Firewire card. With electronics, isolation from electrical current is important and can cause a 60 cycle hum in the USA. In other countries where the current is different the hum is also different.
 
Definitely disable WIFI while recording. Most laptops have a button on them to make this a one click action.
 
Running down the buzz is going to be a challenge but here are some ideas...
- Try your interface on another computer and see if you get the buzz. (You can install Sonar on all the computers you own as long as you only use it on one machine at a time.)
- Try a different Firewire card. I just bought one myself for a new PC.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH&Description=+PCIe+Syba+TI+chipset+Firewire+controller&N=-1&isNodeId=1
- Download Audicity and use it to make a recording with your interface and see if you get the buzz (isolating the problem from Sonar).
http://audacity.sourceforge.net/
 

It's the wireless LAN.

Disabling the wireless land helps but does not fix the issue
Here is an interesting twist on the problem. It happens using all the version of Sonar and using either the fire wire interface or the on board audio which would suggest a more fundamental hardware problem like ram or cpu even a SATA port
The buzzing turned out to be a ground loop so not part of this issue

I'm betting it isn't RAM. It's probably something battery related like the video driver or the battery that I listed above. Have you tried disabling them in the Device manager to see if your situation improves. Don't panic about having them disabled for the purpose of the test.

Its not a laptop it has no battery