I am trying to use F5 Networks VPN Client via a D-LINK WBR-2310 router but it is not working. I opened the ports to Internet, but I can not still use or access my network via VPN.
You will have to open the PPTP Passthrough options in your Firewall. It doesn't work if you just opened the ports. I have attached an image with my router to see exactly what you need to enable in order to use the VPN.