一个用SQLDMO在c#中进行备份，但恢复时数据库在使用中，导致恢复失败！
请教一下，如何做才能正确恢复数据!谢谢了！
错误描述:
Microsoft SQL-DMO （ODBC SQLState: 42000） (0x800A0C1D)
[Microsoft][ODBC SQL Server Driver][SQL Server]因为数据库正在使用，所以未能获得对数据库的排它访问权。
[Microsoft][ODBC SQL Server Driver][SQL Server]RESTORE DATABASE 操作异常终止。

数据还原代码如下,进程我也杀了,可是还是提示数据库正在使用 ：
/// <summary>
/// 还原数据库
/// </summary>
private void btnRestore_Click(object sender, System.EventArgs e)
{

this.Cursor = Cursors.WaitCursor;
this.label1.Text = " 正在进行档案库的数据还原，这可能需要几秒到几十的时间，请稍候...";
this.label1.Visible = true;
this.label1.Refresh();
this.pBar1.Visible = true;
//------------------------------------------------------------------------------------

string fileName = "NorthwindBak";
string filePath = "D:\NorthwindBak";
string remark = "备份测试";

SQLDMO.Restore oRestore = new SQLDMO.RestoreClass();
SQLDMO.SQLServer oSQLServer = new SQLDMO.SQLServerClass();
oRestore.Action = 0 ;
SQLDMO.RestoreSink_PercentCompleteEventHandler pceh = new SQLDMO.RestoreSink_PercentCompleteEventHandler(Step);
oRestore.PercentComplete += pceh;
try
{
oSQLServer.Connect(Common.MySettings.SqlServerName, "sa", "");
SQLDMO.QueryResults qr = oSQLServer.EnumProcesses(-1) ;
int iColPIDNum = -1 ;
int iColDbName = -1 ;

//杀死其它的连接进程
for(int i=1;i<=qr.Columns;i++)
{
string strName = qr.get_ColumnName(i) ;
if (strName.ToUpper().Trim() == "SPID")
{
iColPIDNum = i ;
}
else if (strName.ToUpper().Trim() == "DBNAME")
{
iColDbName = i ;
}
if (iColPIDNum != -1 && iColDbName != -1)
break ;
}

for(int i=1;i<=qr.Rows;i++)
{
int lPID = qr.GetColumnLong(i,iColPIDNum) ;
string strDBName = qr.GetColumnString(i,iColDbName) ;
if (strDBName.ToUpper() == "CgRecord".ToUpper())
oSQLServer.KillProcess(lPID) ;
}

oRestore.Action = SQLDMO.SQLDMO_RESTORE_TYPE.SQLDMORestore_Database;
oRestore.Database = "Northwind";
oRestore.Files = filePath;
oRestore.FileNumber = 1;
oRestore.ReplaceDatabase = true;
oRestore.SQLRestore(oSQLServer);

}
catch(System.Exception ex)
{
Common.ShowMsg("数据还原失败：\n" + ex.ToString());
}
finally
{
oSQLServer.DisConnect();
}

//------------------------------------------------------------------------------------
this.label1.Visible = false;
this.pBar1.Visible = false;
this.Cursor = Cursors.Default;
}

/// <summary>
/// 显示还原进度条
/// </summary>
private void Step(string message,int percent)
{
this.pBar1.Value = percent ;
}