Brother MFC 8840 not waking up

Greetings good fellows and ladies,
A strange problem. The brother MCF 8840 is connected via USB and shared across a wireless network and, from the clients un-informed opinion, a VPN.
The machine works as a fax overnight while the computer is switched off. In the morning when the computer is switched on, the printer remains off-line. un-plugging and re plugging the USB cable results in " Unknown Device" error.
Switching the MFC off/on causes every thing to work again. Brother suggest a USB problem, but apparently this is also happening with the clients Laptop.

any Ideas?

thanx muz