What does log message "As97 AUTH: Duplicate authentication request id=40 already in progress" mean??

[admin_2]

Dialing into (dial-up NT client)a 3640 router with 8 port Async modem card using AAA to authenticate the PPP connection using MS-CHAP, not working. Get above message about a duplicate request in progress, but we know of none?? We have another 3640 in another location with same configuration that works (we do not get the duplicate messages either)

[#2]

Typically this 'duplicate authentication request id=xx already in progress' message means that we already got a authentication request or answer and that we are processing this (contacting the AAA server). If there is some delay there, the remote side will resend the authentication challenge/response and we will print out this message in the debug.

Try to figure out what the problem is with debug ppp negotiation, debug aaa authent, debug radius/tacacs, debug aaa author.

This should tell you where the delay is coming from (probably AAA server not responding)