“dropped” vpn connection

I’m running a SBS server2003 R2 on an ibm eserver x342 8669 at home on Time Warner road runner (broadband). From my office I was able to establish a vpn connection from my xp desktop (not on domain at work) and connect to the server and a client laptop at home. It was working but disconnecting after an undetermined length of time. (1) Is there a timeout I should look for?
Then suddenly the vpn connection disconnect icon came up on the server desktop and I haven’t been able to reconnect since. I have rebooted the server. No ip address changes. Any suggestions? BTW, no problems with Remote Desktop Connection (RDC). But this is not a feasible solution as I need vpn for multiple users and to not tie up desktop for RDC.