I have gone through the article posted in How To Install Virtualbox Guest Additions on Elementary OS - LinuxBabe
I followed the advises and when proceeded for select Devices > Insert Guest Additions CD image . I found Virtual Box error message - “Unable to insert the virtual optical disk /usr/share/virtualbox/VBoxGuestAdditions.iso into the machine ELEMENTARY.”
Therefore, I couldn’t proceed further. I would like to know as to how I clear the deadlock.