|Well, that is an interesting problem and patterns do help to determine causes. This one won't be a quick answer as you've probably guessed. Since there are no patterns, and the vpn establishes sometimes, then there is something that is right sometimes. |
What are the service pack levels of the server and the xp machine?
Is the server part of a cluster?
What type of vpn are you trying to establich - pptp?
Is there another server or device that may answering the xp client requests to establich the vpn? If there are other servers, make only the one server be able to talk vpn to the client.
A sniffer on the server side may tell you if it is receiving the requests at all from the client. Check logs on the server. Find them for a vpn session that worked then compare to times when your xp client cannot connect.
The grass may not be greener on the other side . . . but it just might have less weeds. :-D