segmentation fault on db.open in sqlite Qt5

Question

Inside my small application, I'm using this database frequently to put data. It's working fine but sometime segmentation fault at line db.open() or sometime db.close().

I'm getting free() unsorted chunks:some adress. please any one help.Thanks.

  QSqlDatabase db;
    if (QSqlDatabase::contains())
    {
      db = QSqlDatabase::database(QLatin1String(QSqlDatabase::defaultConnection), false);
    }
    else
    {
       db = QSqlDatabase::addDatabase( "QSQLITE" );
    }
    db.setDatabaseName( "Database/database.db" );
    QSqlQuery qry;
    if(!db.open())
    {
//          qDebug()<< db.lastError();
//          qFatal("Failed to connect.");
        cout<<"database file path problem";
    }
    if(check == "y")
    {


        qry.prepare(  "INSERT INTO serl_num (SERIAL,RESULT)" "VALUES (?,?)");
        qry.addBindValue(_serialNo);
        qry.addBindValue("Abnormal missing file");
    } 
    if(check == "n")
    {

        qry.prepare("select * from serl_num where serial=?");
        qry.addBindValue(_serialNo);
        bool ok=qry.exec();
        if(ok && qry.first())
        {
            qDebug( "serial_number is already in database" );
        }
        else
        {
            QStringList boardNamefile = QString::fromStdString(_boardFile).split('/');
            QStringList boardLayerName = QString::fromStdString(layer).split('.');
            qry.prepare(  "INSERT INTO serl_num (BOARD_NAME,LAYER_NAME,SERIAL,STATUS)" "VALUES (?,?,?,?)");
            qry.addBindValue(boardNamefile.last());
            qry.addBindValue(boardLayerName.first());
            qry.addBindValue(_serialNo);
            qry.addBindValue(0);
        }

    } 


    if( !qry.exec())
    {
        QMessageBox messageBox;
        messageBox.critical(0,"Warning","Database doesn't exist or Database file may be corrupted");
        messageBox.setFixedSize(500,200);
    }
    if(check == "y")
    {
        qDebug( "Updated serial_number as abnormal" );
    }
   db.close();