To resolve this issue :
1. Make sure your Router Support PPTP Passthrough.
2. Make Sure TCP Port 1723 and 47 ( GRE )are Open.
3.Make sure you Allow Connection / Trusted Connection under Your Firewall Application. or Try to Disable Firewall and Re-connect.
If still you are unable to resolve the issue.It means PPTP is blocked by your ISP.So you will require to use L2TP or OpenVPN.
If you require any assistance , please submit ticket from Client Area or email firstname.lastname@example.org