VPN Problems with Leopard Server 10.5.3

I have two servers with exactly the same problem one has been upgraded from a working 10.5.1 server to 10.5.3 and the other was a clean install updated to to 10.5.3. The problem any users in the Open Directory cannot access the VPN the connection is dropped, but if I add the user to the local Directory they can connect with no problems so I have a workaround for now. Here is the info from the logs. 2008-06-17 13:30:35 BST Incoming call... Address given to client = 192.168.1.216 Tue Jun 17 13:30:35 2008 : Directory Services Authentication plugin initialized Tue Jun 17 13:30:35 2008 : Directory Services Authorization plugin initialized Tue Jun 17 13:30:35 2008 : PPTP incoming call in progress from '82.43.148.161'... Tue Jun 17 13:30:35 2008 : PPTP connection established. Tue Jun 17 13:30:35 2008 : using link 0 Tue Jun 17 13:30:35 2008 : Using interface ppp0 Tue Jun 17 13:30:35 2008 : Connect: ppp0 socket[34:17] Tue Jun 17 13:30:35 2008 : sent [LCP ConfReq id=0x1 ] Tue Jun 17 13:30:35 2008 : rcvd [LCP ConfReq id=0x1 ] Tue Jun 17 13:30:35 2008 : lcp_reqci: returning CONFACK. Tue Jun 17 13:30:35 2008 : sent [LCP ConfAck id=0x1 ] Tue Jun 17 13:30:38 2008 : sent [LCP ConfReq id=0x1 ] Tue Jun 17 13:30:38 2008 : rcvd [LCP ConfAck id=0x1 ] Tue Jun 17 13:30:38 2008 : sent [LCP EchoReq id=0x0 magic=0x6394d0bd] Tue Jun 17 13:30:38 2008 : sent [CHAP Challenge id=0x4a , name = "mail.testserver.internal"] Tue Jun 17 13:30:38 2008 : rcvd [LCP EchoReq id=0x0 magic=0xd153511c] Tue Jun 17 13:30:38 2008 : sent [LCP EchoRep id=0x0 magic=0x6394d0bd] Tue Jun 17 13:30:38 2008 : rcvd [LCP EchoRep id=0x0 magic=0xd153511c] Tue Jun 17 13:30:38 2008 : rcvd [CHAP Response id=0x4a , name = "testremote"] Tue Jun 17 13:30:38 2008 : DSAuth plugin: Could not retrieve key agent account information. Tue Jun 17 13:30:38 2008 : sent [CHAP Success id=0x4a "S=919ED8804589EC7DF60B4E79DBD26FC8F17CD527 M=Access granted"] Tue Jun 17 13:30:38 2008 : CHAP peer authentication succeeded for testremote Tue Jun 17 13:30:38 2008 : DSAccessControl plugin: User 'testremote' authorized for access Tue Jun 17 13:30:38 2008 : MPPE required, but keys are not available. Possible plugin problem? Tue Jun 17 13:30:38 2008 : sent [LCP TermReq id=0x2 "MPPE required but not available"] Tue Jun 17 13:30:39 2008 : rcvd [CCP ConfReq id=0x1 ] Tue Jun 17 13:30:39 2008 : rcvd [LCP TermAck id=0x2] Tue Jun 17 13:30:39 2008 : Connection terminated. Tue Jun 17 13:30:39 2008 : Connect time 0.1 minutes. Tue Jun 17 13:30:39 2008 : Sent 0 bytes, received 0 bytes. Tue Jun 17 13:30:39 2008 : PPTP disconnecting... Tue Jun 17 13:30:39 2008 : PPTP disconnected 2008-06-17 13:30:39 BST --> Client with address = 192.168.1.216 has hungup I've tried searching on the problem reported about the plugin problem but have only found a few articles about this which haven't helped any got any ideas. Thanks for your time.