WE have a similar problem on an 897 router , running IOS 15.6(3)M1
May 18 10:48:54.236 AEST: Vi2 IPCP: O CONFREQ [ACKsent] id 2 len 10
May 18 10:48:54.236 AEST: Vi2 IPCP: Address 120.150.217.98 (0x03067896D962)
May 18 10:48:54.236 AEST: Vi2 IPCP: Event[Receive ConfNak/Rej] State[ACKsent to ACKsent]
May 18 10:48:54.252 AEST: Vi2 IPCP: I CONFACK [ACKsent] id 2 len 10
May 18 10:48:54.252 AEST: Vi2 IPCP: Address 120.150.217.98 (0x03067896D962)
May 18 10:48:54.252 AEST: Vi2 IPCP: Event[Receive ConfAck] State[ACKsent to Open]
May 18 10:48:54.256 AEST: Vi2 IPCP: State is Open
May 18 10:48:54.256 AEST: Di1 IPCP: Install negotiated IP interface address 120.150.xx.xx
May 18 10:48:54.256 AEST: Di1 Added to neighbor route AVL tree: topoid 0, address xx.xx.xx.xx
May 18 10:48:54.256 AEST: Di1 IPCP: Route not installed to xx.xx.xx.xx
