Wireless networks disappear from list.

I have got a Sony VGN-SZ61MN running MS-VISTA Home and for some reason I have has instances where the wireless networks absolutely disappear off of the list of networks from the list. However I am very well aware of the fact that the wireless networks are configured properly. Also, I’m a CWNA and thus completely understand wireless network configurations. I am absolutely positive of the fact that the issue is to do with Vista or perhaps the driver. Any clues?