After ungrading network-manager to 1.1.93, though I failed to connect VPN though nm-applet,
however, If I use "pptpsetup .. ; pon .. ; ip route add default .." to establish PPTP VPN, then VPN will be able to connect successfully.
---
So I think it's definitely the bug from network-manager instead of linux drivers or my network environment.
After ungrading network-manager to 1.1.93, though I failed to connect VPN though nm-applet,
however, If I use "pptpsetup .. ; pon .. ; ip route add default .." to establish PPTP VPN, then VPN will be able to connect successfully.
---
So I think it's definitely the bug from network-manager instead of linux drivers or my network environment.