Congratulations, you are receiving new MacOS X version, and fuck you with your PPTP protocol, Apple remove it from OSX Sierra! PROOF HERE!
Are you have the connection to your office or ISP via PPTP? Fuck you and no more! You are crap!
And even if you change connection to L2TP you are obviously going to fuck, because their fucking connection manager using IPSec only. Okay going to FUCK!
Enter to terminal and sudo -s, then:
echo "plugin L2TP.ppp" >> /etc/ppp/options
echo "l2tpnoipsec" >> /etc/ppp/options
And lets Apple going to FUCK!