Thank you, Helen.
I reinstalled Firebird and kept the default dlls (gds32.dll ver
6.3.0.0 & fbclient.dll ver 1.5.0.3773. In my previous description, I
used the type of component such as TIBOQuery, TIB_Transaction and
not the name, just to show which component was used. I fixed the
code as follows:
if not db.Open(SQLUser, SQLPass, SQLDataFile, SQLServerAddress)
then
begin
MessageDlg('Unable to Connect to the Database Server.'
, mtConfirmation, [mbOK], 0);
Exit; {db is a DataModule}
end;
db.IBPatron_.SQL.Clear; {IBPatron_ is TIBOQuery}
db.IBPatron_.IB_Connection := db.cts_IBDatabase1; {TIB_Connection}
db.IBPatron_.IB_Transaction := db.cts_IBTransaction1;
(TIB_Transaction)
if db.cts_IBTransaction1.InTransaction
then db.cts_IBTransaction1.StartTransaction;
try
Mainform.oPatron.db.IBPatron_.SQL.Add('SELECT * FROM STUDENT
WHERE SCHOOL = 2 AND DISTR = 200 ');
Mainform.oPatron.db.IBPatron_.Open;
Result := true;
GoTop;
except
db.cts_IBTransaction1.Rollback;
end;

the .Open is dropping the connection and giving an 335544721 error.
The program makes other selects without problems, except for the one
above.
Thanks.
Horacio C.