VPN PPTP - CTRL: PTY read or GRE write failed

Question

I build my VPN server on digitocean using this script https://raw2.github.com/suyan/Scripts/master/Setup/pptp.sh

However I cannot connect to this VPN server using either my iPhone or Mac. Here is /var/log/syslog says:

Oct 31 18:44:29 VPN pptpd[1422]: CTRL: Client xx.xx.xx.xx control connection started
Oct 31 18:44:29 VPN pptpd[1422]: CTRL: Starting call (launching pppd, opening GRE)
Oct 31 18:44:29 VPN pppd[1423]: Plugin /usr/lib/pptpd/pptpd-logwtmp.so loaded.
Oct 31 18:44:29 VPN pppd[1423]: pppd 2.4.5 started by root, uid 0
Oct 31 18:44:29 VPN pppd[1423]: Using interface ppp0
Oct 31 18:44:29 VPN pppd[1423]: Connect: ppp0 <--> /dev/pts/1
Oct 31 18:44:59 VPN pppd[1423]: LCP: timeout sending Config-Requests
Oct 31 18:44:59 VPN pppd[1423]: Connection terminated.
Oct 31 18:44:59 VPN pppd[1423]: Modem hangup
Oct 31 18:44:59 VPN pppd[1423]: Exit.
Oct 31 18:44:59 VPN pptpd[1422]: GRE: read(fd=6,buffer=b77c8480,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
Oct 31 18:44:59 VPN pptpd[1422]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
Oct 31 18:44:59 VPN pptpd[1422]: CTRL: Reaping child PPP[1423]
Oct 31 18:44:59 VPN pptpd[1422]: CTRL: Client xx.xx.xx.xx control connection finished

Can anyone help?

Answer 1

Changing /etc/ppp/pptpd-options to the following options worked for me:

refuse-pap
refuse-chap
refuse-mschap
#require-chap
#require-mschap
#require-mschap-v2
#require-mppe-128
mppe-stateful