VPN Connection doesn’t get past Verifying

Hi
I have a user who cannot connect via vpn (home to work connection)error 721. No other users are having any trouble.
Client has XP Pro. SP3 using Windows standard connection. PPTP type.
I have tried adjusting MTU but still no luck.
I can connect from my laptop using her account details using the same type of connection.
I have asked her to contact her ISP to check the modem settings, for Port and Protocol allowance, that was supplied by the ISP.
Windows Server 2003 R2 with Routing & Remote Access setup.

Does anyone have any other troubleshooting ideas? I believe it to be something to do with her laptop. NIC drivers are up to date as is WU.

Thanks in advance