Sweet Home 3D is developed on a Mac, so of course it's tested on that system (but rarely under 10.8, since I prefer to work with 10.6 or 10.7).
Maybe you encountered a bug I wasn't aware of. Could you test if it runs when you don't use an external monitor? Could you test your file with the version 4.0 beta and/or send it to [url=mailto:[email protected]]me[/url]?