If you cannot open the guest session and get a VERR_NOT_FOUND VirtualBox error, follow the tips, solutions, and workarounds mentioned below. Check if “VBoxGuestAdditions.iso”n exists Insert Guest ...

If the “Auto-resize Guest Display” is greyed out for you, go ahead and reboot your virtual machine and check if the issue is resolved. In case that doesn’t work, go ahead and restart your VirtualBox.