thoughts without knowing any further details than provided above, a recent systemd update after reading the arch thread.
however, please elaborate further:
-fedora and kernel version
-dkms installed or not
-has it ever worked or is this a new install failing to run
I run VirtualBox 5.1.22 as host with CentOS 7.3 at present so can't say the same has happened to me yet so I don't really know the real solution. Check for the same issue with systemd at https://bugzilla.redhat.com
If no answers are forthcoming here and you can't find the issue on bugzilla, file it as a new bug and provide them with the same information, referencing the arch thread as well.