usb device is not detected through HUB

Hi,

I am working with beagle board and amgstrom distribution.

if we plug the usb device in to usb hub after the hub is plugged into
the beagle board device is not detecting and i got the below message

usb 1-2: USB disconnect, address 2

but if i plug the usb device into hub before the hub is connected to
beagle board then the device is detecting.

Please anyone help me regarding on this.

With Regards,

Raj