Hard to say, maybe the download was corrupted?
The "chmod" command will not say anything, but it will change the attributes of the file to allow execution by the current user. You can check them by "ll atk*", you should see something like "-rwxr--r--" in front of the ATK installer binary. If not, try "chmod u+rwx atk*".
How do you run the installer? You should say "./atk-<fullname_of_installer>" unless "." is in your path. Or double-click it in a file manager.
Run the installer as superuser if you plan to install it system-wide, otherwise don't use "sudo" or "su". If you install as root/su, you may need "chmod a+rwx atk*" instead.