As I mentioned - we normally run an open by MAC filtered WAP. (yes, I know all the issues)
Over the holidays, I installed a 2nd WAP with the lowest common security - WEP All the in house and visiting devices work ok on the WEP network.... except one - There is an XP laptop from school, for a teacher, that runs fine on the Open network, but fails to connect on the WEP network.
The message during the "connection" is... "Windows was unable to find a certificate to log you on to the network ...."
It almost seems like when using the Open network, all is well, but any type of "security" appears to invoke something like 802.11x looking for "validating" of the user connection.