My computer guy who looks after me, when hearing that I have "Fatal error" problems with Sonar X3 Studio, suggested for me to change the drive, running 5400 rpm only, to an external solid state drive, transfer my operating system and of course Sonar to this drive. 
He knows nothing about Sonar, so he suggested to ask here if this is a good idea or not. 
I am with Windows 7, and this problem almost all the time happens when mixing down, changing shapes on envelopes of CC11.
Using GPO 4, EWQL SO, my sound card is M-Audio Delta AP, and controller M-Audio Keystation 61. I run the same set-up on my laptop, when away from home with a Lexicon Alpha interface.
EWQL SO is on a dedicated SSD from EW.
Any help would be most gratefully received..
 
Ted

I don't know if it will fix your problem but you should see a huge performance increase over a 5400 rpm drive. Put Sonar and all your audio stuff on there.

John, thanks for the advise, will do it.
Ted

I'll never buy a standard HD again. SSD all the way.