Network problem validating identity

I then tried installing the supplied Sitecom N adapter, after some problems the network appears but I can't connect, I am told "Windows was unable to find a certificate to log you onto the network" I read several threads that led me to uncheck "Enable IEEE 802.1x authentication for this network" and I actually managed to enter the WPA2 code but this just leads to the message "This connection has limited or no connectivity" and "validating identity".

Home Edition, etc.): You have now succesfully configured Windows XP to connect to eduroam network.I configured the IAS policy to grant access to Domain Computers, Authentication is set to PEAP and uses a private cert issued by our CA, the other profile settings are all default.The client settings on the laptop match the IAS settings and the certificate is definately installed.In order to configure the connection back to Automatic, edit the eduroam profile, go to the Connection tab and check Connect when this network is in range: Figure 14: Setting Automatic connection [1] = If the Wireless Network Connection icon is not present, this may be due to the wireless network manager of your vendor's card taking over from Windows' built-in one (Wireless Zero Configuration).Please refer to the documentation of your vendor's card in order to turn it off as this may interfere with the procedure here documented.

Network problem validating identity