If Vue doesn't ask where to save, it's strange. Are you sure you can save the alpha map? If you rendered at a size that doesn't fit your screen (bigger)you neeb to enable the alpha map to be rendered in the g_buffer, otherwise, you won't be able to save it. You can see it on the screen, but without the option to save. Happened to me a few times, and this is terribly annoying. Now I know I need to enable the g_buffer to be able to save it.