[Serusers] AVP_DB_LOAD ERROR !!!

[iptel]

Hi !
I have a problem with this instruction:
if(avp_db_load("$ruri/username", "s:callfwd/usr_preferences")){
setflag(22);
avp_pushto("$ruri","s:callfwd");
}; 

avp_db_load instruction is always false ... in all condition (field of 
usr_preferences table are correctly compiled )!
It work only in this condition: 

if(!avp_db_load("$ruri/username", "s:callfwd/usr_preferences")) 

nevertheless when the last condition (with a negation) matched avp_pushto 
instruction report this error "avp not found". 

1) Why avp_db_load condition work only whit negation ?
2) Why avp_pushto report this error ? 

Thanks to all.
A.C.