Yes Cisco VPN client with Microsoft CA server certificate able to connect to VPN Concentrator. In order to resolve this issue, ensure that the time is configured properly on both the VPN Concentrator and the CA server. The use of Network Time Protocol (NTP) on both the VPN Conentrator and the CA server allows you to keep time in sync. Clocks in many devices tend to drift a few seconds per day. Exact time synchronization is important for systems on a network so that protocol timestamps and events are accurate. Digital certificates, for example, carry a timestamp that determines a time frame for their validity. An inaccurate time or date can prevent connection.