Problems connecting via WPA/WPA2 Enterprise AFTER upgrade to 10.6

I've seen this on a couple of Macs; a MacBook will work fine connecting to an enterprise WiFi network using either WPA or WPA2 Enterprise. After upgrading from either 10.4 or 10.5 to Snow Leopard these protocols cease to work properly. The upgraded MacBook can connect to WPA or WPA2 Personal networks but nothing involving 802.1x based authentication (This includes the use of LEAP). It looks as if the credentials being passed on to the RADIUS server are incorrect - the authentication server is rejecting the client provided credentials. Despite efforts to manually log in (bypassing any saved preferred network configurations) and deleting all saved preferred networks nothing works. Suggestions?