Bub

I'm not a big fan of memtest86.

 
Neither am I. My current (self-built) system's RAM (respectable quality from a respectable manufacturer) passed memtest86 for 72 straight hours while overclocked about 15%. No errors reported at all.
 
I installed Vista 64bit and had blue screen after blue screen, each time after a few minutes of running. The 0x00xxxxxxx blue screen code number (I forget exactly what it was) indicated the problem was probably in RAM. I reset the RAM back to "normal" speed in BIOS and the blue screens went away.
 
My conclusion is that Vista 64bit is a more demanding and effective RAM tester than memtest86. :-)
 
One tool that can often find RAM/cpu issues (because it thrashes them both while the OS is running) is Prime95 (it won't tell you what the issues are, but it's highly likely to crash if there are any). It's is also handy if you want to stress the cpu out to 100% for an extended period to check on things likewhether the cpu  is adequately cooled if you're running a big (non-standard) heatsink with a big, slow fan for less noise. It is advisable to have an app like speedfan running at the same time though, so you know to terminate Prime95 if temperatures do start to get too high.
 
Another useful (built into Windows) tool is msinfo32.exe (type msinfo into the Run command) which can show you a huge amount of information about what's going on in a PC (hardware, loaded drivers, installed drivers, services, etc.). It can also generate a file that contains a detailed listing of that system information - I suspect getting to the root of why Sonar crashes for some people and not others may require digging through lots of that information -  and still not provide a conclusive answer.  PCs are complicated things and there's no guarantee that any two are identical. :-/