Unable to mount VirtualBox Guest Additions as a guest (Win7 host)

Solution 1:

Finally, I figured it out. Here is how you get arount this. First, load Disk Utility and manually eject the disk in the CDROM, by clicking on the Eject button, after selecting the CDROM device. Then try to remount Guest Additions using the key combination Host + D and voila, Guest Additions should mount successfully.

Solution 2:

I came across this today and it seems it could not be fixed via GUI operations. So I did it via command line. It worked like a charm!

1. Devices -> Install Guest Additions...(it's like insert a cd to cdrom drive)
2. Open a terminal to login the guest machine

3. Type below

   sudo mkdir --p /media/cdrom
   sudo mount -t auto /dev/cdrom /media/cdrom/
   cd /media/cdrom/
   sudo sh VBoxLinuxAdditions.run
   

4. You now can do full screen, shared folder, clipboard sharing, etc