Need to stop & restart PPTP VPN services every few weeks!

Hi Folks, I have an xserve running 10.4.9 up until recently everything had been running fine but recently I've had to restart the PPTP VPN Services every few weeks, due to users getting stuck at Authenticating. From what I have read if you set-up a range of addresses from 192.168.1.200 to 220, each remote connection grabs a new address until it reaches the last IP address, then it starts back at the beginning again. In my case it gets to the last IP address and users fails to connect getting stuck at Authenticating, I've tried changing the IP range with no effect. I have the following services running on the server AFP / Mail / VPN and Web. Has anyone come across this problem ? No Updates have been installed between the server working and not working. Thanks for your time