Backup SQL Database using SMO - Can't find Backup

ok, I am having some problems with SMO.

1. I have followed the instructions here to add the references (connectionInfo, Management.Sdk.Sfc, Smo, SqlEnum)  

2. I have added to my form the following
using Microsoft.SqlServer.Management.Smo;
using Microsoft.SqlServer.Management.Common;

My code is as follows

Server srv = new Server("servername\\databasename");

Backup bkpDBFull = new Backup(); //Namespace name 'Backup' could not be found error. 

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The error is : The type or namespace name 'Backup' could not be found (are you missing a using directive or an assembly reference?)      

Why is it not locating Backup? I am using VS2010 and SQL Server 2008 R2

I was following this code