If, instead of the SQL in the design time, I assign the SQL each time I want to run the cursor, everything works fine!
So seems to me that something is not properly resetted when I close the cursor (Ibo 4.2Ia).
Or maybe I have to call a different method to close the cursor...?

// this works good
crsParamPgm.SQL.Clear;
crsParamPgm.SQL.Add('SELECT PGM_PARAMETRI.A_ID, PGM_PARAMETRI.B_ID, PGM_PARAMETRI.PARAMETRI');
crsParamPgm.SQL.Add('FROM PGM_PARAMETRI');
crsParamPgm.SQL.Add('WHERE (PGM_PARAMETRI.A_ID = ''PGM'') AND (PGM_PARAMETRI.B_ID = '''')');
trsParametri.StartTransaction;
crsParamPgm.APIFirst;
crsParamPgm.Close;
trsParametri.Commit;

// this works good too!!!!!!!!
crsParamPgm.SQL.Clear;
crsParamPgm.SQL.Add('SELECT PGM_PARAMETRI.A_ID, PGM_PARAMETRI.B_ID, PGM_PARAMETRI.PARAMETRI');
crsParamPgm.SQL.Add('FROM PGM_PARAMETRI');
crsParamPgm.SQL.Add('WHERE (PGM_PARAMETRI.A_ID = ''PGM'') AND (PGM_PARAMETRI.B_ID = '''')');
trsParametri.StartTransaction;
crsParamPgm.APIFirst;
crsParamPgm.Close;
trsParametri.Commit;

thanks
Marco Menardi