Can't mount or unmount virtual discs- gives option for "force unmounting"

First, when I restart my computer, it just goes straight to Windows 7, as normal. Is there a separate step to have a selection menu at start-up or does this not apply for VirtualBox runs of Ubuntu?

That's normal. A virtual machine will not come up as an option in the physical host's boot menu. You must start the host OS and the virtual machine manager (hypervisor) before that can happen.

And I get a choice to "Force Unmount" the mounted ISO file within (which is indeed the VBoxGuestAdditions).

• Try ejecting the virtual drive from within the OS first:

• You can also use sudo umount /media/title-of-cd from the terminal.
• Then try unmounting from VirtualBox. Sometimes that may still give you the warning, but just override it so long as you ejected from Ubuntu first.

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