Man, I just ran into that yesterday. For me it was saving the terrain to the browser; sometimes it worked, and sometimes not. Saving to or dragging from the browser would cause a crash. But it doesn't happen every time. I've reported it to Eovia. My work around was to simply create a file with all the terrains in it and then open, save as, and create my scene on it. And it's not just Carrara Terrains, it's ones made in Bryce too. Hope that gets fixed with the WIP patch there doing...