[pptp-server] MS clients cannot connect to PoPToP through ISP

[DaeSooChoi]

Hi
I have a pptp-server running that has no problems with MS windows clients over local LAN connecting, 
but when my MS windows client attempts to connect to pptp-server through dialing-up isp. 

              MS pptp client <------------local lan---------------> Linux PoPToP server  (connection OK)
(problem) MS pptt client <---dialing---> (through)ISP <------------internet------------> Linux PoPToP server ( connected (like below message)but disconnected immediately)

I get errors like below.
--------------------------------
Feb 14 11:34:10 localhost pptpd[5848]: MGR: Launching /usr/local/sbin/pptpctrl to handle client
Feb 14 11:34:10 localhost pptpd[5848]: CTRL: pppd speed = 115200
Feb 14 11:34:10 localhost pptpd[5848]: CTRL: pppd options file = /etc/ppp/options.pptp
Feb 14 11:34:10 localhost pptpd[5848]: CTRL: Client 203.252.3.27 control connection started
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Received PPTP Control Message (type: 1)
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Made a START CTRL CONN RPLY packet
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: I wrote 156 bytes to the client.
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Sent packet to client
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Received PPTP Control Message (type: 7)
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Set parameters to 0 maxbps, 16 window size
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Made a OUT CALL RPLY packet
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Starting call (launching pppd, opening GRE)
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: pty_fd = 5
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: tty_fd = 6
Feb 14 11:34:11 localhost pptpd[5850]: CTRL (PPPD Launcher): Connection speed = 115200
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: I wrote 32 bytes to the client.
Feb 14 11:34:11 localhost pptpd[5848]: CTRL: Sent packet to client
Feb 14 11:34:41 localhost pptpd[5848]: GRE: read(fd=5,buffer=804d8a0,len=8196) from PTY failed: status = -1 error = intput/output error
Feb 14 11:34:41 localhost pptpd[5848]: CTRL: PTY read or GRE write failed (pty,gre)=(5,6)
Feb 14 11:34:41 localhost pptpd[5848]: CTRL: Client 203.252.3.27 control connection finished
Feb 14 11:34:41 localhost pptpd[5848]: CTRL: Exiting now
Feb 14 11:34:41 localhost pptpd[5835]: MGR: Reaped child 5848
---------------------------
in /var/log/pptpd.log
How can I solve "GRE: read from PTY failed ......" 

 Any help appreciated.