备份文件夹问题

当运行下面的代码时，我一直得到"访问被拒绝"，但我对文件夹有完全的管理权限。

{"Cannot open backup device '''''networkDrive'backups'''. Operating system error 5(Access is denied.).'r'nBACKUP DATABASE is terminating abnormally."}

文件夹目标是@"'networkDrive'backups";

我也试过@ '"C: '备份"和@"C: '备份"

    private static string publicConString = "server=myServer;Trusted_Connection=Yes;persist security info=False;connection timeout=120";
    public static void BackupDatabase(String databaseName, String userName, String password, String serverName, String destinationPath)
    {
        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(publicConString);
        ServerConnection connection = new ServerConnection(sqlCon);
        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);