I have problems using my VPN (Virtual Private Network) Some VPNs may not work well with the BT Web Address Help service. If you’re experiencing problems with your VPN you should disconnect from the VPN and then opt out of the BT Web Address Help service in Preferences. You’ll only need to opt out once.
A previously flawless working wireless setup running WPA-PSK2 for months stopped working for no reason, only 2 out of 17 PCs were connecting, 1 wired and 1 wireless, none of the remaining laptops would connect.
After taking a look at the configuration pages I noticed that the router had recieved a BT firmware upgrade as the web pages had completely changed. Suspecting this was the cause of the issue I checked all of the config etc. and could see no problem.
Simply change the wireless channel and all the devices will start connecting again!