USB ports not attached, Linux guest, MacOS host

[at87]

Hello everyone.
I'm running vbox 3.1.8 on MacOs snow leopard using Linux ubuntu 10.04 as guest os. My problem is that everytime I try to access a usb driver, the system cannot mount it (I use the bottom icons to attach my usb drivers correctly configured in the vm using the filters) meaning that there is no automatic procedure and when i try to mount it manually looking for my devices in the /dev folder, I get nothing, It seems that the vm does not expose the drivers to the guest os. The strange thing is that I can select the driver in the bottom bar, although I can select the driver, it is not shown in the os, i it not accessible.

How can i do?

[at87]

Ah, I forgot, additions are installed correctly..