can't pair cellphone

Hello, I've just subscribed to this mailing list because I have a
problem with my bluetooth phone in ubuntu 9.10

I'm trying to pair my phone, but I'm not able to do it.
First of all I tried using the gnome-bluetooth applet, but I failed,
so I started to use the hcitool command in this way

sudo hcitool cc xx:xx:xx:xx:xx:xx
sudo hcitool auth xx:xx:xx:xx:xx:xx

the first command passes, while the second returns this message:
HCI authentication request failed: Input/output error

This is the system log:
Aug 24 13:05:40 yelo3-laptop bluetoothd[4458]: link_key_request
(sba=xx:xx:xx:xx:xx:xx, dba=xx:xx:xx:xx:xx:xx)
Aug 24 13:05:40 yelo3-laptop bluetoothd[4458]: pin_code_request
(sba=xx:xx:xx:xx:xx:xx, dba=xx:xx:xx:xx:xx:xx)
Aug 24 13:05:49 yelo3-laptop NetworkManager:
bluez_manager_bdaddr_removed_cb: BT device xx:xx:xx:xx:xx:xx removed