Here is the image when i double-clicked Terragen 2 Techno Preview.

Then, i tried to made a terrain as simple as possible. It consist of one texture for shader, an atmosphere and a sunlight. I then clicked 'render'. Here the settings i used.

After bout 40 mins rendering, this 'pop-up' thing came, and when i clicked 'ok', TG2 closed.

So, any suggestion?!
btw, I tried to reinstall TG2, and its still the same problem.