The image is unlocked by gimgunlock in mere seconds, not sure what shows using a Mac but with Windows a DOS box opens briefly then is closed automatically. So, you copied the image and dragged it onto gimgunlock.exe and therefore you should have unlocked it. Did you use the OS Mac version from the bottom of the initial post in the link given by Caty, and did you then put the unlocked image back on the Astro?
Sorry, i only can give detailed help to idiots using a PC and that's hard enough.