Windows VPN regelmäßiger periodischer Verbindungsabbruch

Hi,

I've read many threads, where people are talking about problems with VPN, but non of them gave an answer to what I am looking for.

I am using an unsecured wireless network. To actually get internet access, I need to connect to a VPN.
Everything is working fine, when I've restarted my machine. But when I disconnect the VPN and coming back from hibernation the VPN will disconnect every 3 minutes or so and I have to manually reconnect it.

Does anybody know what might be the problem? If you need more information to do an assumption, please let me know.

Best,
STefan