A couple of things:
1. Windows XP laptops that are not Service Pack 3 DO NOT like WPA/AES makes sure you have service pack 3 , if not you care going to have to use another computer or tablet to connect to the Jetpack admin screen and lower the security to WEP Security.
2. "unable to find certificate" This is a cause in Windows XP and you need to disable the IEEE
Go To ---->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 (Note: you may need to restart the computer.)