This same problem is happening to me. I just purchased the family pack and it installed fine on my mac mini, but will not install on my mac pro, I am running 10.6.8.
In your FAQ's, it says, "You need a Mac running OS X 10.6 (Snow Leopard) or higher. While Hazel does clean and organize, Hazel does not do Windows."
I tried deleting the file and dragging in, no luck.
thanks