How to Solve 'Failed to connect to server .\sqlexpress.'

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C#3.0

C#

hi..
When i am trying to take the backup of my database from sqlserver 2005 using c# ,it gives the error as "Failed to connect to server .\sqlexpress.". I have used the code in DBBackup_click event is :

Backup sqlBackup = new Backup();
       sqlBackup.Action = BackupActionType.Database;
       sqlBackup.BackupSetDescription = "ArchiveDataBase:" + DateTime.Now.ToShortDateString();
       sqlBackup.BackupSetName = "Archive";
       sqlBackup.Database = databaseName;
       BackupDeviceItem deviceItem = new BackupDeviceItem(destinationPath, DeviceType.File);
       //SqlConnection sqlCon = new SqlConnection("server=192.168.2.209;database=charity;uid=sa;pwd=pass");
       //ServerConnection connection = new ServerConnection(sqlCon);
       ServerConnection connection = new ServerConnection(serverName, userName, password);
       Server sqlServer = new Server(connection);
       Database db = sqlServer.Databases[databaseName];
       sqlBackup.Initialize = true;
       sqlBackup.Checksum = true;
       sqlBackup.ContinueAfterError = true;

       sqlBackup.Devices.Add(deviceItem);
       sqlBackup.Incremental = false;

       sqlBackup.ExpirationDate = DateTime.Now.AddDays(3);
       sqlBackup.LogTruncation = BackupTruncateLogType.Truncate;

       sqlBackup.FormatMedia = false;
       sqlBackup.SqlBackup(sqlServer);  /* Here, It throws the error */

can anyone tell me , how to solve this error?