Yes, it's the free version we're using, downloaded yesterday evening from Sourceforge.
We tried it again to day on another Mac, and the same thing happened.
But we HAVE found a way around it:
A question arose during lunch: Have you tried copying the program off your Macbook, and run it on the Mac Pro?
So we did, and it worked. The obvious solution.
I have uploaded the damaged app in case you want to have a look at it.
Sweet Home 3D app damaged
cec
