备份数据库时连接数据库出错,该如何解决

备份数据库时连接数据库出错
错误信息为：
[Microsoft][ODBC SQL Server Driver][DBNETLIB]SQL Server 不存在或访问被拒绝
[Microsoft][ODBC SQL Server Driver][DBNETLIB]ConnectionOpen (Connect()).

代码如下：

C# code

SQLDMO.Backup oBackup = new SQLDMO.BackupClass();            SQLDMO.SQLServer oSQLServer = new SQLDMO.SQLServerClass();            try            {                oSQLServer.LoginSecure = false;                oSQLServer.Connect("127.0.0.1", "sa", "123");                oBackup.Action = SQLDMO.SQLDMO_BACKUP_TYPE.SQLDMOBackup_Database;                oBackup.Database = dbName;                oBackup.Files = @"backup\" + backupDBName + ".bak";                oBackup.BackupSetName = backupDBName;                               oBackup.BackupSetDescription = "数据库备份";                oBackup.Initialize = true;                            oBackup.SQLBackup(oSQLServer);                           }