DB Filtering BLOB (RTF) Fields

I have a Pardox database and I use TQuery to join tables. In TQuery I have BLOB field (with RTF document). I need to filter my database by this BLOB field. I tried with QueryFilterRecord(aDataSet: TDataSet; var Accept: Boolean) event. When I need to access to BLOB field I get this message:
---------------------------
Debugger Exception Notification
---------------------------
Project KatalogZapisa.exe raised exception class EDatabaseError with message 'Query: Cannot access field 'Sadrzaj' in a filter'. Process stopped. Use Step or Run to continue.
---------------------------
OK   Help  
---------------------------
But when I access another field which isn't BLOB field, everything is OK.

My code looks like this:
 
procedure TData.QueryFilterRecord(aDataSet: TDataSet; var Accept: Boolean); var
  s: TStream;
begin
        s := TStream.Create;
        try
            s := aDataSet.CreateBlobStream(aDataSet.FindField('Sadrzaj'), bmRead);
            MainForm.Re.Clear;
            MainForm.Re.Line.LoadFromStram(s);
            Accept := MainForm.Re.FindText(FindWhat, 0, Length(MainForm.re.Text), []) <> -1;
        finally
            s.Free;
        end;
end;
 
Can anybody help me?