使用buyVM的128m VPS搭建VPN，顺利工作了大概一个星期，之后VPN就无法连接，求问

本地的日志是这样

Mon May 27 15:10:37 2013 : PPTP connecting to server 'xxx.xxx.xxx.xxx...
Mon May 27 15:10:37 2013 : PPTP connection established.
Mon May 27 15:10:37 2013 : PPTP set port-mapping for en0, interface: 4, protocol: 0, privatePort: 0
Mon May 27 15:10:37 2013 : Using interface ppp0
Mon May 27 15:10:37 2013 : Connect: ppp0 <--> socket[34:17]
Mon May 27 15:10:37 2013 : PPTP port-mapping for en0, interfaceIndex: 0, Protocol: None, Private Port: 0, Public Address: xxxxxxx, Public Port: 0, TTL: 0.
Mon May 27 15:10:37 2013 : PPTP port-mapping for en0 inconsistent. is Connected: 1, Previous interface: 4, Current interface 0
Mon May 27 15:10:37 2013 : PPTP port-mapping for en0 initialized. is Connected: 1, Previous publicAddress: (0), Current publicAddress b71b0d76
Mon May 27 15:10:37 2013 : PPTP port-mapping for en0 fully initialized. Flagging up
Mon May 27 15:11:07 2013 : LCP: timeout sending Config-Requests
Mon May 27 15:11:07 2013 : Connection terminated.
Mon May 27 15:11:07 2013 : PPTP disconnecting...
Mon May 27 15:11:07 2013 : PPTP clearing port-mapping for en0
Mon May 27 15:11:07 2013 : PPTP disconnected


问题应该出在这行
Mon May 27 15:11:07 2013 : LCP: timeout sending Config-Requests

但是不清楚到底是什么原因，有大牛知道什么情况么？
谢谢。