Does Sonar crash when you load ANY project, or just one particular project?
(make a backup of the project prior to doing the following)
What happens if you open the project in Sonar's 'Safe Mode'? (To do this, hold down the Shift key when you tell Sonar to load the project you want to test, and Sonar will use its Safe Mode to give you the chance to either load or skip each plugin that is part of the project. This can be a great way to isolate issues, as well as possibly a last chance at getting the project open when there are issues caused by plugin problems).
Does the failing project have any 32-bit plugins loaded in a 64-bit Sonar?
Does the Sample Rate of the project match the Sample Rate the audio interface is using?
What kind of audio interface are you using, if any? (Focusrite, AudioBox, M-Audio, EMU, ASIO4ALL, etc.)
Is it possible you have a USB audio interface that might have gotten plugged into a USB 3.0 port? (some interfaces freak out unless you use USB 2.0 ports for them).
What Web browser are you using? (Internet Explorer?, Firefox?, etc.)
What version of Windows are you running? Is it up to current maintenance levels?
Does Sonar fail if you temporarily disable your antivirus software prior to launching Sonar? (do not access the internet if you do this, and make sure to enable the antivirus software right after testing this).
Sonar has been really stable, as far as crashes go, so whatever is happening is most likely something specific to your system - some plugin failing or an issue with ASIO4ALL - if you use that, or maybe Windows maintenance is not current and this is causing problems, etc.)
Are there any Windows errors logged in the Event Viewer? Any error message shown when things crash?
Thanks - we will try to help you get this figured out.
Bob Bone