[Users] radius accounting problem

[tele]

hi all,

reading acc modules README:

     * There is no session accounting -- OpenSER maintains no
       sessions. If one needs to correlate INVITEs with BYEs for
       example for purpose of billing, then it is better done in
       the entity which collects accounting information.
       Otherwise, SIP server would have to become
       sessions-stateful, which would very badly impact its
       scalability.

so it's impossible to do radius accounting for billing purpose?
i need a B2BUA for that? any hints?

anyway i'm trying radius acct

this is my problem:

 0(25586) ACC: transaction answered: call_id=d3cd352603256e75 at ua1, 
totag=360701152, from="222" <sip:222 at mysip>;tag=d288f8fc7ea68a04, 
i-uri=sip:111 at ss:5060, method=BYE, o-uri=sip:111 at ss:5060, 
fromtag=d288f8fc7ea68a04, code=200, to=<sip:111 at mysip>;tag=360701152, 
uid=n/a, userpart=111
 0(25586) ERROR: acc_rad_request: radius-ing failed

i've activated all possible debug but i received only this message about 
radius.
i'm trying to activate debug for radiusclient

this is my setup:

FreeBSD 6.1
OpenSER 1.0.1
radiusclient-0.5.2

thank you