Last night I had this strange issue. But first, here is my system spec:

i5 processor, 4GB RAM, Win 7 HP 64 bit
Sonar X1D Expanded
ASIO4ALL 2.11 beta
 
When I open a project and press play I get distorted sounds, I mean unbearably distorted, as if there is a distortion effect on every channels. I stop the project, open the preference page in Sonar and open the ASIO4ALL window, close it, press play. Voila.. everything is back to normal. Interesting to note that I didn't make any change on ASIO4ALL windows. No change at all, no buffer setting, nothing. I just opened and closed it. That's all. I didn't have to do it for the entire session afterwards. At times, the project plays but without any sound. If I keep pressing stop and play for 2-3 times it play okay.

Some funny thing going on, not sure what it is. This is the first time I encountered something like this. As I said, it's not a showstopper. I am really close to a deadline hence haven't done much troubleshooting. Point of posting this is to find out if anyone had this problem at all.

Do you have audio snap enabled and possibly changed the tempo? I've seen 99.9 db distortion on every audio track as of X1 D. Reproducible by Cakewalk. Happens when audio tracks are enabled for Audio snap, then change the tempo, then click around the timeline and distortion. Loud too! You might try WDM mode just to see although they usually recommend ASIO. Disable audio snap on all audio tracks and see if that helps...

Nah.. no Audiosnap. All are midi tracks. Like I said I didn't do anything to the project at all. No tempo change, nothing. Just opened it and pressed play button, that's all. Tried WASAPI but didn't get good latency as ASIO4ALL so changed it. I will try WDM mode as you suggested and will report back. 

Quick question
On this preference page:
MIDI > Playback and Recording > Playback section > Prepare using 250 millisecond buffers

Do I need to make any change? May be increase from 250 to some other value.

This is just a hunch as the same project plays without any artifacts on my Sonar 32 bit installation.