ISA 2006 PPTP VPN connection bouncing between initiating and closed.

Hi,

I am faced an issue where my ISA Server isn't playing ball with PPTP clients. Not sure what has gone wrong, as this was working at one point.

Following is the output I am seeing from the PPTP client:

Nov 615:02:31cdcsdaemon.debugmdm_emukillall pptp >/dev/null 2>&1
Nov 615:02:30cdcsdaemon.debugpppd[1192]sent [LCP ConfReq id=0x1 ]
Nov 615:02:27cdcsdaemon.debugpppd[1192]sent [LCP ConfReq id=0x1 ]
Nov 615:02:24cdcsdaemon.debugpppd[1192]sent [LCP ConfReq id=0x1 ]
Nov 615:02:21cdcsdaemon.debugpppd[1192]sent [LCP ConfReq id=0x1 ]
Nov 615:02:18cdcsdaemon.debugpppd[1192]sent [LCP ConfReq id=0x1 ]
Nov 615:02:18cdcsdaemon.noticepppd[1192]Connect: ppp1 <--> /dev/pts/0 Nov 615:02:18cdcsdaemon.infopppd[1192]Using interface ppp1 Nov 615:02:18cdcsdaemon.debugpppd[1192]using channel 11


It is a cellular router (CDM-882seu for those who want to look it up). I've checked the usual cultprits - namely, GRE capability, SIM card failure, service issues from provider side of both the cellular service and our ISP to no avail. Have also tried with multiple devices, and even just using the Windows XP VPN client.
The connection isn't even getting to a point where I can see authentication attempts.

Any thoughts?

Cheers!