Update: Found threads here, and at M-Audio's site, with same problem...reading and researching.

Happy Friday! I recently got some help in Hardware Forum and it turns out I was using the ASIO4ALL driver - which I didn't remember downloading a while back - oops. Anway, have ASIO installed and selected in Preferences now.

However, from within Sonar, if I select ASIO Panel and attempt to change the latency in M-Audio's Control window, which pops up, this error message displays...

'Fast Track Pro Panel'

"An invalid operation was attempted on an active network connection."

...and the latency cannot be changed.

If I close Sonar and then open M-Audio's Control, I can change the latency, but anything less than 512k samples results in stuttered playback with clicks-n-pops, etc.

So, within Sonar the latency slider and buffer size box are greyed out and the ASIO Panel button is active. But, there is another place within Preferences where you can select a driver. It's under Audio>Sync and Caching - 'Record Latency Adjustment (samples)' That is currently set to 'ASIO4ALL v2 (1 in, 1, out)', but when I select the only other option, 'M-Audio USB ASIO (2 in, 2 out)' and Apply, it always defaults back to the ASIO4ALL option.

It looks like ASIO4All is still installed on your machine.
It is a fairly robust driver, and its mere presence on the machine will interfere with you other ASIO drivers. It must be uninstalled.
A while back, I had downloaded ASIO4All to help somebody out with using it for the factory sound card.
The backlash was that it crippled the native ASIO drivers for my E-MU sound card.
ASIO4All is good for its intended purpose, but causes problems if it is not needed.

I didn't actually 'uninstall' ASIO4ALL - just selected ASIO - but I will as soon as I'm back at the DAW.
 
Thanks.