Problems -- rad_verify: invalid signature (err=2)！ （shared secret is incorrect）

[Xiaochen]

Hi all,
I am using Fedora 12 and Freeradius 1.2.9 to do some COA test. 
When AAA sends Disconnect-request to my AGW, the AGW reply with a
Disconnect-ACK, and my MS disconnects.
But the rad_verify says: 
-----------------------------------------------------------------------
Received Disconnect-ACK packet from clinet 100.1.6.4 port 3799 with invalid
signature (err=2)! (shared secret is incorrect.
-----------------------------------------------------------------------
In fact the shared secret is correct!!!
My disconnect packt.txt is like:
-----------------------------------------------------------------------
Acct-Session-Id="00000001"
Calling-Station-Id="001E310008CC"
User-Name="wimax at zte.com"
X-Ascend-Session-Svr-Key="0123456789"
NAS-IP-Address=100.1.6.4
NAS-Identifier=CATR
WiMAX-DM-Action-Code="0xffff"
WiMAX-AAA-Session-Id="00000002"
-----------------------------------------------------------------------

I don’t know how to solve this problem, can you please give any
suggestions?

Thanks a lot!

Xiaochen @ a WiMAX Lab