virtualbox.org

I Installed VB (virtualbox-5.0_5.0.16-105871~Ubuntu~trusty_amd64.deb) on Linux Mint 17.1
then I install CentOS 7, CentOS-7-x86_64-DVD-1503-01.iso, as VM.

I then start the CentOS 7 VM and login.
And from inside the VB, I click VB's menu item "Devices" > "Insert Guest Additions CD Image.... "
But I have this error message after I clicked "Insert Guest Additions CD Image.... ":

Could not mount the media/drive
'/usr/share/virtualbox/VBoxGuestAdditions.iso'
(VERR_PDM_MEDIA_LOCKED).

Result Code:
NS_ERROR_FAILURE (0x80004005)
Component:
ConsoleWrap
Interface:
IConsole {872da645-4a9b-1727-bee2-5585105b9eed}
Callee:
IMachine {f30138d4-e5ea-4b3a-8858-a059de4c93fd}

How do I get VB to find the guest addition or how do I download the guest addition iso into the correct place for VB to install as guest addition iso?
Keep in mind that the CentOS 7 VM is running while I try to "Insert Guest Additions CD Image.... "

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I found these on my Linux Mint host (not inside the VM):
/usr/share/virtualbox $ ls -al
total 59912
drwxr-xr-x 5 root root 4096 Mar 11 14:40 .
drwxr-xr-x 332 root root 12288 Mar 11 11:17 ..
drwxr-xr-x 2 root root 4096 Mar 11 14:40 nls
drwxr-xr-x 2 root root 4096 Mar 11 14:40 rdesktop-vrdp-keymaps
-rw-r--r-- 1 root root 1236823 Mar 4 10:22 rdesktop-vrdp.tar.gz
drwxr-xr-x 3 root root 4096 Mar 11 14:40 src
-rwxr-xr-x 1 root root 1505 Jun 9 2015 VBoxCreateUSBNode.sh
-rw-r--r-- 1 root root 60063744 Mar 4 10:25 VBoxGuestAdditions.iso
-rwxr-xr-x 1 root root 4161 Jun 9 2015 VBoxSysInfo.sh
-rwxr-xr-x 1 root root 4350 Oct 11 2014 x11config.pl

/usr/share/virtualbox $ file VBoxGuestAdditions.iso
VBoxGuestAdditions.iso: # ISO 9660 CD-ROM filesystem data 'VBOXADDITIONS_5.0.16_105871'

Since I have VBoxGuestAdditions.iso, why do I still have the error?
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As a side topic, can we run a VM with a different guest addition, an example would be to run a lightweight Linux Mint VM with a CentOS guest addition ?



Thank you.