My shared folder/clipboard stopped to work for some reason (probably due to a patch installation on my virtual machine).
sudo mount -t vboxsf Shared_Folder ~/SF/
Gave following result:
VirtualBox: mount.vboxsf: mounting failed with the error: No such device
The solution for me was to stop vboxadd and do a setup after that:
cd /opt/VBoxGuestAdditions-*/init
sudo ./vboxadd setup