In an Ubuntu virtual machine in VirtualBox, there was an error installing the Guest Additions Client Enhancement Pack: Assigning media virtual discs xxx\vboxsguestadditions.iso to Virtual PC XXX lost

Excerpt from: http://www.crifan.com/virtualbox_ubuntu_install_guest_addtions_fail_could_not_mount_the_media/

Problem

In the Ubuntu virtual machine in VirtualBox,

Install guest additions, error:

Assigning Media virtual Discs Xxx\vboxsguestadditions.iso

To the virtual computer XXX failed. Whether you want to force the unload to allocate the media.

Could not mount the media/drive xxx\vboxsguestadditions.iso (verr_pdm_media_locked)

"Resolution Process"

1. Others have similar problems:

Unable to mount VirtualBox guest additions as a guest (Win7 host)

Can not Mount guest additions in guest Linux

Unable to mount the CD/DVD image
/usr/share/virtualbox/vboxguestadditions.iso on the
Machine Perciseforwine. Would you-to-force mounting
of this medium?
Details

Result Code:
Ns_error_failure (0x80004005)
Component:
Console
Interface:
Iconsole {db7ab4ca-2a3f-4183-9243-c1208da92392}
Callee:
Imachine {22781af3-1c96-4126-9edf-67a020e0e858}

2. Reference:

Unable to mount VirtualBox guest additions as a guest (Win7 host)

Go, manually eject the corresponding disc:

You can then see the prompt, which has popped up:

3. Then re-operate again:

Installation enhancements for Devices:

Can mount the CDROM normally.

Then after entering the password, you can go to install:

After installation, enter the return key. The installation window disappears.

Summary

The first time you mount a vboxadditions cdrom, this error will occur.

A manual pop-up, and then reinstall Guest Additions, will do.