WPA/WPA2 secured wireless connection fails for two minurtes for every hour of use.

Question

Hello.
I have a brand new ThinkPad T500 2055-A16 with Windows Vista Business. I have a WiFi connection problem. It is not a signal strength problem, as it doesn't work even if I place the computer right next to the access point with no other wireless equipment near by.
None of my other computers experience this problem. I even bought another ThinkPad T500 2055-A16 at the same time as this one, and that does not have the problem either. The problem is when I connect to a network using WPA2-PSK or WPA-PSK. The connection works fine for half an hour, an hour or two hours, but then without warning, the connection is lost and it is not possible to reconnect for half a minute, a minute or two minutes. The exact times vary. When I switch the network to use WEP or no encryption, everything works fine. But I don't like to use no encryption and I cannot use WEP because I have other computers in my home which does not support WEP.
I had this problem right from the beginning the first time I used the computer. I have tried many things like disabling power management or IPv6 and other things suggested by my ISP, but it did not change anything, so I switched them back to their default value. I have also tried to update the driver for the Intel(R) WiFi Link 5100 AGN card, but that didn't help the problem. The problem became slightly less annoying when I uninstalled Access Connections, because Vista would then reconnect as soon as it could, whereas I in Access Connections would have to continuously press the connect button until it succeeded. But the problem is still a real pain.
Some pieces from the Windows Event Viewer, which I think looks interesting (these occur regularly at exactly the same timestamps as when the connection is lost):
 Profile match: Success
 Pre-Association: Success
 Association: Success
 Security and Authentication: Fail
0x00048005 and 0x0003800b
Result of diagnosis: Problem found
 Issue referred to: L2Sec Helper Class
I also see the following message on my access point's log, which also occur at exactly the times when the connection is lost:
1x:00216b4d7ee6:logout
(The number match the MAC address of my computer)
The only other message which is logged on my Access Point when all log options are enabled is "Time initialized by NTP server".
How can I solve this problem so that I can have undisrupted wireless Internet access?

Answer 1

Edit: Actually my other ThinkPad T500 2055-A16 also fails in the same way, but my ThinkPad SL500 2746-9BG and my Medion laptops works fine, also running Vista.