I already set the registry not to allow to turn off power of the USB hub. Thanks anyway.
It sounds like you know about the power management- and using a quality externally powered USB hub. There is one other common cause- a USB device that is not 2.0 compliant being connected or a problem USB device connecting or disconnecting from the same hub. Is anyone slipping another device in or out of the hub? is there anything else on the hub?
I will look into the registry settings,