Radius Authentication

[network_4]

We have HP-UX server on which xtradius is running, users from ras use this server for authentication. But from today when i am trying to login from ras i am not able to do so. From radius too when i am trying to do radtest it's giving me below error:

+++++++++++Error Message+++++++++++++++++++++
radtest infiniet5 infi05 a.b.c.d 2 testing123
Sending request to server a.b.c.d, port 1812.
radrecv: Reply from host a.b.c.d code=3, id=198, length=62
Reply-Message = "\015\012Access denied (external check failed)."
Access denied.
+++++++++++++++++++++++++++++++++++++++++++++++++++

Actually radius uses ldap for authentication.

and when i am using radldaptest from radius i am able to authenticate. So what could be issue is this some AV pair mismatch.

Please let me know why this "external check failed" appears and what could be possible reason.