I just downloaded the demo, but it won't play. http://i.imgur.com/tgaW1k8.png
Wow.... we have never seen this one before, have you tried redownloading the demo? Which version did you download?
I tried both windows demos, and both showed that same screen. I redownloaded both not long after but the same thing happened.
Edit: Tried redownloading again to no avail. Neither of the windows demos are working for me.
I could be wrong, but it looks like another tool you have downloaded is opening the exe. Have you tried running as admin, or in compatibility mode? It probably wont fix a default program opening the exe, but who knows. It could also be that the zip file isnt downloadling properly, and the file is corrupt.