Oudakerk:
When using 3rd Party disk mounting apps like UltraISO and Magicdisk and Demon Tools, ya can only unmount the disks using that program, for instance with UltraISO, you right click on the Drive, and it will show "UltraISO" in the drop down box, put the mouse on that, and it will extend out to "Eject"
But with both MagicDisk and Demon Tools, you actually have to click on the icons for the programs in the tray and then right click on the appropriate drive that pops out, and hit "Eject" from there.
In windows 8, all ya gotta do is right click and hit Eject. Another thing you have to consider, even if you right click on an ISO image with Windows 8 and it says "Failed to Mount" - Check it anyway, most of the time it has mounted despite the error message.