Not to a necro a thread, but since this is one of the first results when searching for the software crashing.. If it's previously worked with different settings, load some known settings, go to preview, and turn off travel moves and retraction, then switch your settings, close S3D and reopen. My issue started when I turned off retraction in ooze control to rule it out on Z axis scarring (ooze control was definitely the culprit). Since there weren't any retract moves, it got confused and crashed.
On a side note, the programmer who's doing the coding for this needs to add in "try...(normal button behavior) catch ex as exception msgbox ex" to the button that swaps to preview mode to help clean up issues like this, assuming they're using c# or vb.net.