Guest System: Fedora 19 64-bit
Guest additions successfully installed using: VBoxLinuxAdditions.run
Behaviour: Boot proceeds to systemd reporting: Reached target Graphical Interface. At this point the boot stalls.
Error line in Xorg.0.log: (EE) Failed to load module "vboxvideo" (module does not exist, 0)
The solution appears to be replacing the link: /usr/lib64/xorg/modules/drivers/vboxvideo_drv.so with the file pointed to by the link.
Note that the link and target are both on the same partition.
The problem appeared this week after installing updates.
I suspect the problem may be a security issue, possibly selinux related, but I didn't investigate further.
Perhaps someone more knowledgeable could provide an explanation?