Cant conect via USB

[Oier Lauzirika]

When I try to run a example in my NXT break shows this error:

Traceback (most recent call last):

  File "C:\Users\oier.oier-lauzirika\Desktop\nxt-python-2.2.2\examples\cnc.py", line 10, in <module>

    b = nxt.find_one_brick()

  File "C:\Python27\lib\site-packages\nxt\locator.py", line 112, in find_one_brick

    for s in find_bricks(host, name, silent, method):

  File "C:\Python27\lib\site-packages\nxt\locator.py", line 43, in find_bricks

    for s in socks:

  File "C:\Python27\lib\site-packages\nxt\usbsock.py", line 84, in find_bricks

    for bus in usb.busses():

  File "C:\Python27\lib\site-packages\usb\legacy.py", line 333, in busses

    return (Bus(),)

  File "C:\Python27\lib\site-packages\usb\legacy.py", line 329, in __init__

    self.devices = [Device(d) for d in core.find(find_all=True)]

  File "C:\Python27\lib\site-packages\usb\core.py", line 846, in find

    raise ValueError('No backend available')

ValueError: No backend available

Thank you