I am trying to use boot camp assistant and one of the options is to Create a Windows 7 install disk but it is grayed out. It states that I need a USB flash drive and a Windows 7 ISO image. Which I have both of, but the option not selectable? I erased the Flash drive and tried both Mac OS Extended (Journaled) and MS-DOS (FAT). And I currently have the .ISO on my desktop. What am I doing wrong here?