Networking Via Usb Cable: "ifconfig" Works, But "usb Reset" Occurs

my c1000, which runs Zubuntu RC1(ubuntu 8.04 supplied by Omegamoon), meet a problem:

"ifconfig" do works, but "USB reset" occurs as soon as connecting the USB cable to the host PC.

at first, "ifconfig usb0 up xxx.xxx.xxx.xxx" fails, so I unload the modules:

$modprobe -r ohci_hcd <= unload usb host module

then

$modprobe pxa27x_udc
$modprobe g_ether
$ifconfig usb0 192.168.129.201 netmask 255.255.255.0 up

after that, "ifconfig" shows the following two interfaces:

------------------
lo ...
... <=loop interface

usb0 Link encap:Ethernet Hwaddr XX:XX:XX:XX:XX....
inet addr: 192.168.129.201 Bcast: 192.168.129.255 Mask:255.255.255.0
UP ...
...
...
... <= usb0 interface appears!
------------------

everything seems OK. However, when I attach my c1000 to a PC (Linux & Windows XP) via the

usb cable:
on my Linux laptop, "dmesg" and "/var/log/messages" shows NOTHING;
and on my Windows XP laptop, NOTHING happens.
(I used to do usb networking on c1000/pdaXrom, "dmesg" on Linux will show the USB device messages and windows XP will "find new hardware".)

and,

on my c1000/Zubuntu, "/var/log/messages" shows:

----------
...
.... Zubuntu kernel: pxa2xx-udc pxa2xx-udc: USB reset
----------

I'm confused, what's wrong? any solution?

I have to connect the zubuntu to the internet to get any packages installed. please help me!

Thank you.