I’m out of idea.
Did you use the latest WLan driver from here:
http://aps2.toshiba-tro.de/wlan/?page=downloads
Did you also edit the power saving setting for the power plant which is used if the ac adaptor is disconnected?
Do also this:
Device manager -> WLan card -> properties -> power management tab
Here uncheck the option which allow the system to disable this device to save power.