"Cannot resolve symbol" error in VS with SMO

Question

Microsoft.SqlServer.ConnectionInfo.dll
Microsoft.SqlServer.Smo.dll
Microsoft.SqlServer.SmoEnum.dll
Microsoft.SqlServer.SqlEnum.dll
Microsoft.SqlServer.Management.Sdk.Sfc.dll

i have referenced all the above assemblies in my C# project but when i type

   Microsoft.SqlServer.Management.Smo.Backup bkpDatabase = new Backup();

i get an this error "canot resolve symbol Backup" even when i have below using statements

using Microsoft.SqlServer.Management.Smo;
using Microsoft.SqlServer.Management.Common;

Answer 1

i had not referenced Microsoft.SqlServer.SmoExtended in my project in addition to the assemblies mentioned above.