Comment 127 for bug 263963

I encoutered exactly the same problem as Michele Nasti (see above : 2008-11-24).
The initial association with the WPA APworks fine but after some time the laptop loose connectivity and the is no way to reconnect to the AP. (authentication timedout). At this point, only a restart of the AP would make things work again.

I solved this problem by disabling "protected Mode" in the router configuration. Router is a belkin 54g.
The protected mode is described as :

"As part of the 802.11g specification, Protected mode ensures proper operation of 802.11g clients and access points when there is heavy 802.11b traffic in the operating environment. When protected mode is ON, 802.11g scans for other wireless network traffic before it transmits data. Therefore, using this mode in environments with HEAVY 802.11b traffic or interference achieves best performance results. If you are in an environment with very little--or no--other wireless network traffic, your best performance will be achieved with Protected mode OFF."

This problems seems not related to authentication, since I reproduced it with WEP and without any authentication.
The problem also does not occur under windows XP. So I believe there is a driver bug behind this.