Linux – Problem connecting to PPTP VPN in Ubuntu 9.10

I have a VPN client configured for using PPTP under Ubuntu 9.10 (the alpha version, but fully up to date). The configuration has everything enabled except for EAP (I found I had to uncheck that to make it work).

It worked fine until Tuesday of this week. It now fails with a message: "VPN Connection Failed".

The message in /var/log/messages when it worked on Tuesday is:

Plugin /usr/lib/pppd/2.4.5//nm-pptp-pppd-plugin.so loaded.  
pppd 2.4.5 started by root, uid 0  
Using interface ppp0  
ppp0 <--> /dev/pts/2  
CHAP authentication succeeded  
MPPE 128-bit stateless compression enabled  
local  IP address XXX.XXX.XXX.XXX  
remote IP address XXX.XXX.XXX.XXX  
primary   DNS address XXX.XXX.XXX.XXX  
secondary DNS address XXX.XXX.XXX.XXX  

Now it has changed to:

Plugin /usr/lib/pppd/2.4.5//nm-pptp-pppd-plugin.so loaded.  
pppd 2.4.5 started by root, uid 0  
Using interface ppp0  
ppp0 <--> /dev/pts/3  
Modem hangup  
Connection terminated.  
Exit.  

I'm using Ubuntu 9.10 alpha; I'm using the standard network-manager applet to configure it (but have also tried kVPNc and manual configuration). The VPN is working fine– I can connect to it using an XP virtual machine running on the system.