problem with MD5 encrypted secret

[Guido]

Another question about secret...
How can I configure freeradius to work with MD5 secret ? The secret now, is 
coming MD5 encrypted and I see the following error:

---rad_recv: Accounting-Request packet from host 192.168.1.12:1813, id=0, 
length=772
---Received Accounting-Request packet from 192.168.1.12 with invalid 
signature!  (Shared secret is incorrect.)
---Server rejecting request 11.


Regards,

Guido