When I un-freeze a track which is connected to an EastWest Orchestra Gold synth instance, Sonar crashes consistently. Probably 50% of the time, an un-freeze causes the crash, requiring a system reboot. This can happen on any track/instance. Anyone know why this is or what I can do about it?

jkoseattle...Probably 50% of the time, an un-freeze causes the crash, requiring a system reboot. This can happen on any track/instance. Anyone know why this is or what I can do about it?

Bummer.  Until such time this problem is figured out, I'm sure you've considered just bouncing instead of freezing, but maybe didn't want to do that as a work-around. 
 
As someone who never freezes but always bounces, let me encourage you.  Since you like to freeze, that means you want to be able to undo and go back to a MIDI track to do more editing.  Unfreezing is theoretically instant, but deleting a bounced track and then bouncing again after editing really doesn't add more than a handful of seconds to the process.  Bouncing a track for a 3 minute song takes approximately 3 seconds.  Doesn't freezing take the same amount of time?
 
Naturally you want to figure out why you're crashing with freeze - But I wanted to point out that bouncing could work just as well for you.  If you try that for now, hopefully that doesn't also crash your computer!
 
Randy
 
 

That's a great idea. It's messier - I liked the ability to essentially replace the midi track with the audio by freezing, and now I have another track to deal with, but it works great, and the "fast bounce" works, whereas with freezing I always had to turn the fast bounce off. Thanks, great idea!

jkoseattle
That's a great idea. It's messier - I liked the ability to essentially replace the midi track with the audio by freezing, and now I have another track to deal with, but it works great, and the "fast bounce" works, whereas with freezing I always had to turn the fast bounce off. Thanks, great idea!

Good, glad that works for you.  Like I said in my 1st reply, I never freeze, only bounce.  That's an "old school" approach, but it's so straight-forward, easy and fast. 
 
From your quote above, I see you're using "simple instrument tracks" - something else I'm too old school to use.  As I'm working on a project before the mixing stage, I always have my MIDI tracks lined up together - I mean the actual MIDI tracks, and the associated audio tracks are together below those.  When I'm ready, I bounce all the tracks to audio before starting to mix.  I make much use of the Track Manager to remove things I don't need to see, so when I'm done with MIDI, I mute, archive, and remove all those tracks from view, both the MIDI and audio tracks that are conduits from the soft synths.  And of course the soft synths are also disconnected when I don't need them anymore.  At mix time, all I have on my screen are the audio tracks.  Works great for me.
 
Randy

Have you tried converting you Simple Instrument Track to split Midi/Audio and then freeze?
 
I seem to remember SIT's can cause a few problems with freezing, or maybe it's just another false memory......