I had laptop running Windows XP SP2 that was trying to connect to a wireless network the other day. It would fail each time with an error bubble popping up in the system tray with the following message ”Windows was unable to find a certificate to log you on to the network [SSID]” .
I wasn’t using a certificate for the wireless access point in question, so I thought this was odd that there was a certificate error. I checked the wireless setting and realised that there weren’t all the available types on encryption that there should be, so I hit the Microsoft web site for an update, and found this KB article here.
This installs a patch to enable you to use the more recent types of WPA encryption that weren’t out when SP2 was release for Windows XP.
After applying the patch and rebooting, the error bubble was gone.