Problem with the attribute "Message-Authenticator"

["yao guoxian" <yaoguoxian@gmail.com>]

    I write a program to send Access-request packet to the Radius server. The packet format is as follow:
    __________________________________________________________
    |  code = 1      |       ID = 1     |    Length = 73 ( 0x 00 49 )                   |
    __________________________________________________________
    |     16 bytes authenticator                                                               |
    __________________________________________________________
    |     user_name = "test"                                                                   |
    __________________________________________________________
    |     chap_password                                                                         |
    __________________________________________________________
    |      eap_message = "pdsicygx"                                                       |
    __________________________________________________________
    |      Message_authenticator                                                             |
    __________________________________________________________
    The Message_authenticator is calculated as follow:
     Message_authenticator = HMAC-MD5 (code ,ID, Length,16 bytes Authenticator, user_name,chap_password,eap_message) ,
using the shared secret between NAS and radius server , in this case ,"testing123". 
    While sending "chap" packets without the  "eap_message" and "Message_authenticator" gets "Access request
" , sending packets like above gets  response from radius server as follow:
    rad_recv: Access-Request packet from host 202.117.7.223:1408, id=1, length=73
    Received packet from 
202.117.7.223 with invalid Message-Authenticator!  (Shared secret is incorrect.)
    Server rejecting request 1.
    Finished request 1
    Going to the next request
    --- Walking the entire request list ---
    Waking up in 1 seconds...
    --- Walking the entire request list ---
    Waking up in 1 seconds...
    --- Walking the entire request list ---
    Sending Access-Reject of id 1 to 
202.117.7.223:1408

    Segmentations of the "Radiusd -X " are as follow:
    ...
    Module: Loaded eap
    eap: default_eap_type = "md5"
    eap: timer_expire = 60
    eap: ignore_unknown_eap_types = no
    eap: cisco_accounting_username_bug = no
    rlm_eap: Loaded and initialized type md5
    rlm_eap: Loaded and initialized type leap
    ...
    Can the "eap_message" attribute  be set randomly, in my packets, "pdsicygx"?  Is it right to calculate "Message_authenticator" as I did?
   

Regards
Guoxian