why 'sql' is not supported in Authentication method?

[xieshengluo]

I follow the instruction given by http:///www.frontios.com/freeradius.html and add 
'sql' in the authentacation section. But when I restart the  radiusd, I am told that 
SQL modules aren't allowed in 'authenticate' section--they have no such method.
Thanks for your help!.+-�w��˛���m��˛���m�zm�����y��v+���?�+-����m�