Cisco VPN client issue

Hi, I have a VPN client that having connectivity issue, she is using "vpnclient-win-msi-5.0.01.0600-k9.exe" to connect to a PIX515, I tried her laptop with 3 different lines everything is fine but from her home she can only start and login to VPN client but no data is passing after that, and she cannot use remote desktop. The only difference between her Internet line and other line is that line is a PPPoE line, and other lines(working lines) are cable TV lines. I changed the MTU size using VPN Client software option but didnt help. She is using Windows Vista. Any idea how to resolve this issue? Ali