May 16 09:01:40 server pptpd[4137]: CTRL: Client xxx.xxx.xxx.xxx control connection started
May 16 09:01:40 server pptpd[4137]: CTRL: Starting call (launching pppd, opening GRE)
May 16 09:01:40 server pppd[4138]: Plugin /usr/lib64/pptpd/pptpd-logwtmp.so loaded.
May 16 09:01:40 server pppd[4138]: This system lacks kernel support for PPP.  This could be because the PPP kernel module could not be loaded, or because PPP was not included in the kernel configuration.  If PPP was included as a module, try `/sbin/modprobe -v ppp'.  If that fails, check that ppp.o exists in /lib/modules/`uname -r`/net. See README.linux file in the ppp distribution for more details. 
May 16 09:01:40 server pptpd[4137]: GRE: read(fd=6,buffer=611860,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
May 16 09:01:40 server pptpd[4137]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
May 16 09:01:40 server pptpd[4137]: CTRL: Client xxx.xxx.xxx..xxx control connection finished