In the Finder, select the Go > Go To Folder... menu item, type the folder ~/Library/Containers/com.eteks.sweethome3d.SweetHome3D/Data/Library/Application Support/eTeks/Sweet Home 3D (tilde included) and remove the recovery folder that you'll find there.
If you could send [url=mailto:[email protected]]me[/url] the file it contains, it might help me better understand your problem, and maybe fix a possible bug.