SQLDMO中调用PercentComplete触发事件时出错

相关代码如下：  
public  string  StrServer,StrUser,StrPassword,StrDatabase,StrBackupPath;  
private  SQLDMO.Backup  MyBackup;  
 
this.Load  +=  new  System.EventHandler(this.FrmBackup_Load);  
MyBackup.PercentComplete  +=  new  SQLDMO.BackupSink_PercentCompleteEventHandler(MyBackup_PercentComplete);     //提示出错的行 
 
private  void  FrmBackup_Load(object  sender,  System.EventArgs  e)  
{  
           SQLDMO.SQLServer  SqlServer=new  SQLDMO.SQLServerClass();  
           SqlServer.LoginSecure=false;  
           SqlServer.Connect(StrServer,StrUser,StrPassword);  
           MyBackup=new  SQLDMO.BackupClass();  
           MyBackup.Database=StrDatabase;  
           MyBackup.Action=0;  
           MyBackup.Files=StrBackupPath;  
           MyBackup.Initialize=true;  
 
           progressBar1.Value=0;  
           progressBar1.Maximum  =  100;  
           MyBackup.SQLBackup(SqlServer);  
           progressBar1.Value  =  100;  
 
           MessageBox.Show("数据库备份完成","系统消息");  
}  
 
private  void  MyBackup_PercentComplete(string  Message,  int  Percent)  
{  
           progressBar1.Value  =  progressBar1.Maximum  *  (  Percent  /  100);  
}  
 错误提示：  
未处理的“System.NullReferenceException”类型的异常出现在  DbBackup.exe  中。  
 
其他信息:  未将对象引用设置到对象的实例。  
 
 
 
请问该怎么改？？