Cisco VPN, WinXP and Vaio Laptops

In June of 2005, we experienced some VPN issues. All of our Sony Vaio laptops running WinXP Pro would no longer connect to our VPN. Sometimes the connections is established, but the resources on the other side of the connection cannot be accessed. Sometimes no connection can be made.

We are using Cisco client 4.0. All other users of the VPN are connecting.

We have uninstalled and re-installed the client several times. Turned off the firewall. No resolution at this point.

Does anyone have an idea as to what may have happened?