at first I would like to apologize for my unusual english - I am not native english speaker.
I am running OS X 10.8.2 Server, which is configuered as a VPN server for my clients (who use FileMaker globally across VPN).
The path of network is: server->router->internet. This link of course has static public IP by provider and router has open necessary ports (1701,1723,4500,500).
Actually, everything works fine - server runs, clients who connect with protocol L2TP are able to connect and run everything what is needed.
I have to say that on my windows clients I had to change registry settings for right working L2TP. But, everything works fine.
Unfortunately some clients must use older protocol PPTP, because of their IT politics (for example small schools). Don't ask me why, but I can't do anything with it.
So I switched the setting from "L2TP only" to "L2TP and PPTP" and reconfigured all users as "network users" because PPTP has different meaning of users.
The result is: Windows clients are not able to connect to VPN with PPTP, only L2TP. L2TP is usable with registry edit, which is ok. But I need to solve this for PPTP clients. By the way OS X clients are able to work with both protocols without any problems.
I have found out that on windows clients return error messages for example 807. In the end, for me it looks like that they are not able to initialise connection at the start (somewhere in windows or on the way windows client->router/server...) because I don't see any attempts on my OS X Server in Console or logs.
There are some topics about it on google, which talk about opening port 1723 and enabling GRE protocol 47...
I understand that this is Apple Support Community, so windows clients might be out of topic here.
But I hope that some of you might dealed with this issue.
I am able to post logs, screenshots...
Thank you very much.