RouterOS做VPN连接后自动断线

qq3994086

认证使用的free radius；
提示中有关于断线的原因是NAS-Error，这个是什么意思啊？应该怎么修改？

radius的日志信息如下：
Mon May 25 18:05:29 2009
        Service-Type = Framed-User
        Framed-Protocol = PPP
        NAS-Port = 303400
        NAS-Port-Type = Virtual
        User-Name = "vpntest"
        Calling-Station-Id = "219.237.242.160"
        Called-Station-Id = "222.218.124.77"
        Acct-Session-Id = "815003de"
        Framed-IP-Address = 172.1.2.254
        Acct-Authentic = RADIUS
        Acct-Status-Type = Start
        NAS-Identifier = "www.77vpn.com.cn"
        NAS-IP-Address = 222.218.124.77
        Acct-Delay-Time = 0
        Acct-Unique-Session-Id = "529e14ab53b90ca2"
        Timestamp = 1243245929
        Request-Authenticator = Verified

Mon May 25 18:05:29 2009
        Service-Type = Framed-User
        Framed-Protocol = PPP
        NAS-Port = 303400
        NAS-Port-Type = Virtual
        User-Name = "vpntest"
        Calling-Station-Id = "219.237.242.160"
        Called-Station-Id = "222.218.124.77"
        Acct-Session-Id = "815003de"
        Framed-IP-Address = 172.1.2.254
        Acct-Authentic = RADIUS
        Acct-Session-Time = 0
        Acct-Input-Octets = 124
        Acct-Input-Gigawords = 0
        Acct-Input-Packets = 10
        Acct-Output-Octets = 106
        Acct-Output-Gigawords = 0
        Acct-Output-Packets = 10
        Acct-Status-Type = Stop
        Acct-Terminate-Cause = NAS-Error
        NAS-Identifier = "www.77vpn.com.cn"
        NAS-IP-Address = 222.218.124.77
        Acct-Delay-Time = 0
        Acct-Unique-Session-Id = "529e14ab53b90ca2"
        Timestamp = 1243245929
        Request-Authenticator = Verified