Thank you for the suggestion. I checked the length of my downloaded file and it is correct. Before downloading it again, it occurred to me to try 'Run as administrator' and it worked I guess I should have tried that in the first place.

I downloaded SweetHome3D-3.4-windows.exe and when I run it under Windows 7 it always crashes with the following:
Problem signature:
Problem Event Name: APPCRASH
Application Name: SweetHome3D-3.4-windows.tmp
Application Version: 51.52.0.0
Application Timestamp: 2a425e19
Fault Module Name ...