Check the routes on the "Routing" configuration page (This facility is available by clicking on the "Internet Settings" menu followed by "Routing" and then the "Static" menu item on the right.)
i.
There should be 5 routes shown.
ii.
One route for interface eth0.
iii.
Two routes for interface ppp0.
iv.
Two routes for interface ppp1.
If there are not 5 routes, it is possible the one of the following conditions exist:
i.
PPTP is not enabled.
ii.
The credentials on the PPTP Configuration page are incorrect (IP address / Username / Password).
iii.
If you see the message: "The synchronous PPTP option is not activated" or "CHAP Authentication Failure", then the credentials are incorrect.