Ok here's another test:
turned on latency mon a few minutes, platinum was open, then started playing midi piano, lost piano audio with a dropout of audio engine after about a  1min, I can see audio engine icon on Transport unlit and off, I wasn't recording just playing piano with transport stopped, all was caught on latency mon in this image below. After I hit stop on Latency Mon I looked at "Stats" and copied and pasted the results in report 4.RTF  I'm not sure how much of that text I should put into a forum post, so if anyone wants all or part of it let me know.
 
 

Ouch. Yup, sure looks like a USB issue. Well, not USB per se, but rather something that's plugged into a USB port. What other USB devices do you have? Any that can be temporarily disconnected for testing?

gswitz
So, your USB Latency is a bit high. I'm curious which device is causing it.
 
You can trouble shoot this by starting latencymon and then try unplugging various USB things (including your mouse). Test to see if there is a particular device that is causing it to be high. You see mine is at .18 and yours is at .77.
 
I also noticed ataport.sys...
https://msdn.microsoft.com/en-us/library/windows/hardware/ff551332%28v=vs.85%29.aspx
 
Do you have a an older ATA drive in your system? Just curious.
 
I once had a mouse issue with a logitech mouse. I just had to download Logitech's driver and use that instead of using the default Windows driver which didn't have good latency specs.

I unplugged these USB's  - I-lok Dongle for Ivory, Dongle for Vienna Instruments, USB keyboard (this is 2nd keyboard for vocalists to record themselves in vocal booth). The only other USB is my MOTU midi interface. I unplugged all except the MOTU, opened an old project in Platinum, hit play and got a dropout in a min or so. Sometimes when I first open a project I get a dropout early on and then no more dropouts.
 
I do have an old 80 gig IDE HD that has XP, in case I need to use XP. I have 
440 gig - boot
3T - data
1T - audio
2T - Ivory
220 gig - Win7 for dual boot
 
 For USBPORT.SYS the value for highest execution varies a lot. It's usually near the top of the list.
 I'm not sure what to look for in Latency Mon. This values usually starts around .17 and went up to .25 during the test I have above. It make take a while running the test to make it up to .77.  Let me know what you want me to look for with unplugging these USBs.

Hola, yo he tenido algun problema parecido, y se me soluciono cambiando de proyecto, los instrumentos virtuales no se copiaron bien desde otro ordenador y la informacion midi era muy confusa, en el piano roll.

Hi, I had similar problem, and I solved Changing Project, Virtual Instruments are not copied either from another computer and midi information very confused, in the piano roll

I'll have translated with google translator, my English is very loose, just wanted to help, when the system goes wrong it is a brown

The USB system used 22 seconds of CPU that time. The number of DPCs for the Motu midi still looks high. With nothing playing, it shouldn't have so much to say. Is there any way to check your system without it? E.g. unplug it and play a project that doesn't send to any h/w synths.

bvideo

The USB system used 22 seconds of CPU that time. The number of DPCs for the Motu midi still looks high. With nothing playing, it shouldn't have so much to say. Is there any way to check your system without it? E.g. unplug it and play a project that doesn't send to any h/w synths.

Unplugged all USBs, including midi interface and iLok for Ivory. Started LatencyMon, In Platinum, hit play on song I mixed today which took 45 min with no dropouts. This song has Ivory and Superior drummer. I didn't delete Ivory, even though I did unplug the iLok for Ivory. Sonar didn't seem to like this because I got dropout at 1:41, hit play after a min or so, dropout again at 3 min, start over then dropout at 20 sec. I also saved the Stats If you need them in addition to this picture below.

Unplugged all USBs, including midi interface and iLok for Ivory. Since the previous test wasn't very good with Sonar looking for the midi interface and Ivory, this time I Deleted Ivory, Start LatencyMon, then sonar, hit play, runs 5.5 min no dropout, rewind hit play, message comes up saying "no MOTU midi interface should sonar route midi to another and stop transport?" NO.  Plays for a min then dropout, hit play it goes about 3 min and dropout. I have the Stats saved for this one below also.

There is no single "highest execution time" to cause a dropout, and now USBPORT is running at a sane level. There is still a lot of disk activity.
 
At this point, the disk is still a possible culprit: ataport.sys has a high ISR and DPC count. Although its total execution time is low, it does show there is a lot of disk activity going on.
 
Has the overall syndrome of your dropouts changed? Earlier you reported no dropouts except when playing or recording from your keys. Now without keys there are still a few dropouts.
 
Did latency mon stop reporting problems? If so, the remaining problem might be disk I/O. For your 32-bit system, paging could be an issue if there are a lot of processes that need to run and compete with Sonar for memory. Or reading samples could be an issue, or reading a lot of audio files. For disk I/O, the Resource Monitor report could be more useful. Also, did you try bitflipper's suggestion to freeze your sample-driven instruments?
 
What audio buffer size are you using now? Does a higher setting help? How about disk I/O buffers? The manual/help has info on how to tune and analyze disk I/O problems (Edit > Preferences > Audio - Sync and Caching, and Edit > Preferences > Audio - Driver Settings
 
Back to the MOTU topic: with the MOTU plugged back in but no equipment connected, is the Latency Mon report more sane? How about hooking up your equipment in small steps, starting with just the P200 out going to the MOTU in. Play a few notes into Sonar for a minute and check the L-M report for high counts from motumidi64.sys. What is the first hookup step that causes crazy USBPORT.sys numbers?