Virtualbox share folder

hi to all
i'have a w7 pc and virtualbox with latest live cd installed (2.5.0)
i try to share w7 folder and ubuntu folder
i installed guest addition from terminal and i created a folder on w7
then i created a folder on ubuntu
when i try to mount the ubuntu folder from terminal, i have an error :

/sbin/mount.vboxsf : mounting failed with the error : no such device

i installed guest addition from terminal:
sudo apt-get update
sudo apt-get install build-essential linux-headers-$(uname -r)
sudo apt-get install virtualbox-ose-guest-x11

Anyone help me ?
Alessandro

hi
i read the latest live cd instructions and i think that the mistake is
on the operating system. My system is w7 64 bit and i read the system
for latest live cd is 32bit
Now i've installed the old emc2 2.3.5 with 8.04 ubuntu system and all ok.
Is it possible?
Sorry for my bad english......
Alessandro

They are both 32 bit, so it is not that.