after 20 minutes:
 [2013-10-22 19:42:46] usb_write error on avalon_write
 [2013-10-22 19:42:46] usb_write error on avalon_write
 [2013-10-22 19:42:46] usb_write error on avalon_write
 [2013-10-22 19:42:46] usb_write error on avalon_write
 [2013-10-22 19:42:46] usb_write error on avalon_write
after cgminer restart:
2013-10-22 19:44:29] avalon detect (1:23) failed to initialise (incorrect device?)

it could be broken usb hub.....
invastigating now

my line:
--bitburner-voltage 1300  --avalon-options 115200:12:10:28:420 --queue 3 -G --avalon-fan 80