Hello.
I have same problem on two computers with windows 7 prof x64. The file can't be opened. The error message says "Can't open home 'test.sh3d'". The file was created on this computer.
On a PC running Windows 2003, the same file can be opened without any problems.
P.S If the "*.sh3d" contains only walls and rooms, there is no problem. If I add a piece of furniture, a door or a window - the file can't be opened.