I spent more then hour to solve this so I’ll post the solution.
Problem: on mounting shared folder named “common” in Ubuntu as guest OS over Mac Os X as host OS
sudo mount -t vboxsf common /media/common
I got the error:
/sbin/mount.vboxsf: mounting failed with the error: Invalid argument
quote folders’ names!
sudo mount -t vboxsf "common" "/media/common"