Hi

THANKS TO YOU GUYS FOR HELPING ME OUT...

Picture cache.... that's a first for me... ? Where do I fnd it and is it possible to set some parameters for it ?

CTRL + open or SHIFT + Open for safe mode. I'll definately try both.....

Windows update - no. The computer is not connected to the internet. I installed Win 8 some weeks ago and had all updates from the installation point in time. The video driver is (still) the latest.

Yes... X2A - I have been running that since it was released.

I suspect the A&H drivers to play some part in this problem even though it seems to be related to Sonar only by the way it crashes. I never had this problem with my previous mixer (Phonic). On the other hand I didnt have a complex project like this then.... 
But... WHO knows... ( This is what I really dont like about DAW's - you can work on a problem for weeks and weeks - and I even used to Work in the software business... (dont tell anyone))

rgds Bruno

The location of the picture cache is defined in Edit > Preferences > Audio Data "Picture Folder" entry. The size of the cache is controlled in the AUD.ini PicCacheMB variable. This can be adjusted in Edit > Preferences > Configuration File.

i didn't see anyone mention buffer size. you have 45 tracks with 10 busses. i wonder if your audio engine is shutting down. I have had this issue in the past, I increase the buffer size and that usually helps. I have a couple of huge projects, and i have had to freeze a few of the soft synths and tracks with resource heavy plugs.  Just a thought. Good luck!!!

Yeah, refreshing the picture cache is a first for me, too. Never had to do this in any other DAW before Sonar Xn. Seems like a band-aid.

  I don't see it as a band-aid at all. IIRC that limit of the picture cache can be increased unless that's old thinking in these 21st century apps, larger file sizes and what we demand of our DAW software. OP...keep us updated. Carry on....

Like I said, never had to do this before Sonar. And I know I have the hardware horsepower to not have random pictures fall off occasionally without warning. I dunno. Carry on...

To the OP: I would suspect you should be getting "dropouts", and obviously you should see indicators of how hard the DAW is working in the Performance Module. If you don't see any issues there, I'm banking on something else within Windows is consuming resources. 

Ctrl+Alt-Del and see your Task Manager to see what Processes are hogging your CPU, meanwhile watching the Performance Module in Sonar. Gray/White-screening is indicative of Windows having trouble, not the DAW. Otherwise, you should see RAM, CPU, or I/O going to 100%, in Performance Module if the session is overloading Sonar. 

Maybe that could help. 

It has been a while but I recall I had a project that would crash and it ended up being one plugin out of many.  If you are at wits end you might want to try taking out all your plugins and adding them back one by one to see which one it is. 

I was using a Syba TI chipset PCI firewire card. It was the cause of all my crashes with Sonar X2. I removed it and no more crashes.

The reason I said safe mode is it loads your project without any plug ins.
to me this sounds like a plug in if its not hardware related.
because the project was working but now its not.
serious. look for a plug in not jiving.