One of the differences between the installer/Java Web Start version and the Jar executable version is the max amount of memory required by Sweet Home 3D to run.
Please, run SweetHome3D-2.0.jar with the following command (use Windows Start menu > Execute dialog box and replace "C:\path\to\" by the exact location where SweetHome3D-2.0.jar can be found):

javaw -Xmx512m -jar C:\path\to\SweetHome3D-2.0.jar

then with the following command:

javaw -Xmx1024m -jar C:\path\to\SweetHome3D-2.0.jar

and report here if both commands worked correctly.
Thank you for your help.