- Install sstp-client and libsstp-client0 via PPA
sudo add-apt-repository ppa:eivnaes/network-manager-sstp
sudo apt-get update
sudo apt-get install sstp-client
sudo apt-get install libsstp-client0
- Try installing network-manager-sstp and network-manager-sstp-gnome also from this PPA
sudo apt-get install network-manager-sstp