Vista loses WiFi key repeatedly

Hi. Let me pass you some info before going to the specific problem:

Laptop: Toshiba Satellite U 300 / Core Duo @2.00 GHz with 1G Ram
Operating system: Vista Home Premium
Router: Linksys model WRT54GS version 3.0. Firmware version is v2.07.1
dated Feb 26, 2004.
Network config: non-broadcasting, WPA-TKIP with a 63 characters long,
randomly generated key.
There are other 4 laptops connected to the same network, all of them running
on Windows XP.

For some strange reason, after Stand-by or hybernation the laptop running on
Vista looses the network key (all others running on XP have no problem).

I have reset the wifi network several times making sure everything is OK but
the problem persists. FYI both the "connect automatically" and "connect even
if not broadcasting" options are selected.

Before posting this I've checked with Linksys about upgrading the firmware
but they responded that it is not necessary since mine is OK in terms of
security patches, etc.

I look forward to hearing your suggestions to solve my problem. Tks so much !