I looked all over the Internet for a long time to find this answer. Once I discovered it, I decided to post it here on HMR so that everyone can have it.
The problem arises in Windows XP while trying to connect to a secured network, often on a D-link router.
While trying to connect a new computer wirelessly, an error comes up stating that “Windows was unable to find a certificate to log you onto the network (Network name here).
Here’s how to fix it if it is WEP encryption…
Start –> Programs –> Accessories –> Communications –> Network Connections –> Right-click your Connection and select Properties –> Click on the Authentication tab –> Disable / uncheck the option IEEE 802.1x authentication for this network. Now, try to connect to your Wireless network; are you able to? (Note: you may need to restart the computer.)
If it is WPA encryption, make sure you are using the TKIP type and it is set correctly in both the router and the new machine’s connection.