connection string with sql server express

I'm using SQL server 2012 express and I'm having trouble with my connection string when I tried to access my database via Classic ASP page.

I don't know what is wrong with my connection string.

Driver={SQL Server};server=DTWEBCLONE2008R\SQLEXPRESS; database=ClientData; Uid=sa;Pwd=Hello123;

Please help. Thanks!

<%@ Language=JavaScript%><%

try{

 var cn = Server.CreateObject("ADODB.Connection");
 cn.Open("Driver={SQL Server};server=DTWEBCLONE2008R\SQLEXPRESS; database=ClientData; Uid=sa;Pwd=Hello123;");
 cn.Close();
 cn = null;

}
catch(e){
Response.Write(e);
}

%>