can't share folders after yum update

[virtualsomething]

Running windows 7 host w/fedora 20 guest. Setup shared folders and they worked fine for a long time, then they stopped working recently. When trying to mount the folders, get the error "/sbin/mount.vboxsf: mounting failed with the error: No such device" Tried all online suggestions and no luck.

Eventually narrowed it down to working with fresh Fedora 20 install but the error occurs after a "yum update".

So if I have a VM that's been updated and boot from "Fedora with Linux 3.11.10-301.fc20.x86_64", it works fine. But if booting with the latest, "Fedora 3.16.3-200.fc20.x86_64) 20 (Heisenbug)" the shared folders don't work

[virtualsomething]

What additional information would be required.

[Frank Mehnert]

Please execute /bin/lsmod | grep vbox in the guest and check if the VirtualBox kernel modules are loaded, in particular the vboxsf kernel module.

[Robert Muil]

I'm seeing this also (although it's never worked for me on this machine).

    $ lsmod |grep vbox
    vboxguest             235809  6 

I'm running Ubuntu 14 as host, so it seems independent of host OS.

Host and guest are both 64bit.