I’m sorry, this is caused by a known issue. It only happens on a few older graphics cards, but it is something we want to address and find a fix for.
Right now there’s nothing I can do to help, other than suggest installing Animation Paper on another computer – if that is a possibility. I know that’s probably not an option. 🙂
We will hopefully have it fixed within the next couple of alpha releases (alpha 4 or 5).