I get this one happening to me about once a week (on a busy week - maybe 15ish hours of work). I'm using the Edirol UA25EX. X1d, i72600, 8gig Ripjaws X, decent Asus MoBo etc. So I don't know... I'm using Asio as WDM is not a happy camper. Doesn't appear to be any plugs or specific behaviour that causes it. I should make a detailed log each time it happens.

Got some supposed super task-kill program to try. I'm waiting for another crash now though so I can try it. I've always just restarted except once I kept trying things for 10-15 mins and it cleaned up without a restart. So maybe that would happen every time, but it's faster to just restart.

Boo :(

I too have had this issue, and as mentioned it was due to my Delta 1010. I forgot what I did to resolve it. I have since moved on to a MOTU and haven't had an issue since. David

I occasionally have the same issue running a Delta 1010 along with an Axiom 61...just to be clear here...are we saying the sonarpdr.exe process is hard to kill in task manager due to M-audio drivers or are we saying an M-audio product/drivers are causing the issue in the 1st place? 
Thanks very much,
Randy

sonar, for whatever reason, is unable to release the driver... if it's an external soundcard (e.g., usb) then power cycling that unit is faster than fully rebooting the pc, as sonar will be able to close when the device is off and drivers unloaded :-) some of these regular questions should be stickies, or combined into a faq post

I had this a lot with my older Asus MB and M-Audio Axiom 49. Now that I have upgraded Motherboards, I think it went away.

i have this all the time happen to me as well during projects. very frustrating indeed.
i can only associate it with the usage of plugins, some of the built in ones, and UAD ones.
i too agree that this is likely my midisport drivers, even though they are recent and i keep my computer up to date and clean.
in X1, the power off doesnt allow Sonar X1 to close like it used to.
SOMETIMES in 8.5.2 Sonar would eventually quit (after a power cycle of the MIDISPORT) but not so recently.

only solution is to reboot.

hmm... sounds like it's mostly interfaces causing issues. Maybe the Axiom is safe? And I'm curious about the comment regarding just powering down the device. Essentially if I were to encounter this problem just disconnecting the Axiom might allow the process to close normally? I really want that keyboard. I'd hate to have to start my search all over again. :-/

Beep, I'd say if we find out that the drivers aren't causing the issue in the first place (Sonar not responding to where we have to close and restart it) but just taking time to release the drivers after closing sonar....then maybe that shouldn't be a deciding factor because they are good controllers for the money if you ask me.
Now if we find they are indeed causing the issue in the first place then to hell with M-Audio!....come to think about it, they were pretty slow getting their 64 bit drivers released

@randy... Yeah, I've been hesitant to buy M-Audio stuff in the past and I never really knew why (I think it was the affiliation with Avid that irked me) but now that I'm here and reading up on stuff it seems that gut instinct may have been at least somewhat correct. Seems like there are a lot of strange issues like this surrounding their stuff at least in regards to Sonar. I just can't afford the fancy Roland stuff at the moment or I'd go that route. IDK... maybe it'll work out but 10 minute long screw ups is pretty bad. At least I'm aware of it now so if something does go wonky I won't be completely stumped. Ugh... it's always something, eh?

I'm pretty sure you can use the Axiom as a MIDI device (as in, connect it with a MIDI cable to your interface rather than with an USB cable to your computer), in that case there should be no keyboard-specific drivers in use anyway