PGresult and for-cycle

I develop this code:

PQclear(sol);
psqlDisconnettiDB(DB);

ris=(abbonamenti_t **) calloc(nabb,sizeof(abbonamenti_t *));
sol2=(PGresult **) calloc(nabb,sizeof(PGresult *));

for (i=0;i<nabb;i++)
{
ris[i]=(abbonamenti_t *) calloc(1,sizeof(abbonamenti_t));

st1=astrcpy("SELECT rivabbval.PrezzoLit, rivabbval.PrezzoEur,
rivabbval.DataInizioValidita, rivabbval.DataFineValidita,
rivtipabb.Descrizione FROM rivabbval, rivtipabb WHERE
rivabbval.IDrav=");
st2=astrcat(st1,key[i]);
free(st1);
st1=astrcat(st2," and rivtipabb.IDrta=rivabbval.IDrta;");
free(st2);

DB=(PGconn *) psqlConnettiDB0("mulino_db");
psqlBeginTransaction(DB);
psqlLockTable(DB,"rivvalarr","ACCESS EXCLUSIVE MODE");
{FILE *E; E=fopen("problem.txt","a");fprintf(E,"BOOM 2-1 SQL abb
-%s-\n",st1);fclose(E);}

sol2[i]=PQexec(DB,st1);

free(st1);
/***/
ris[i]->lire_abb=atof(PQgetvalue(sol2[i],i,0));
ris[i]->euro_abb=atof(PQgetvalue(sol2[i],i,1));
ris[i]->inizio_abb=astrcpy(PQgetvalue(sol2[i],i,2));
ris[i]->fine_abb=astrcpy(PQgetvalue(sol2[i],i,3));
ris[i]->abbo=astrcpy(PQgetvalue(sol2[i],i,4));

PQclear(sol2[i]);
psqlDisconnettiDB(DB);
}

the 1st loop is OK, the 2nd produces a core and stops at /***/.
Why ?

Could you help me ?
-----------------------------------
Gianluigi Roveda
E-mail: roveda(at)omega(dot)it

Omega Generation S.R.L.
Via Montebello, 2 40121 Bologna
TEL 051/4210311
FAX 051/4211039