error: Namespace name 'EntityState' does not exist

Hello,

I have a error:

The type or namespace name 'EntityState' does not exist in the namespace 'System.Data.Entity'

But, I have added reference System.Data. Kindly answer me.

using DAL.Model;

using System;

using System.Collections.Generic;

//using System.Data;

using System.Data.Entity;

using System.Linq;

using System.Linq.Expressions;

using System.Web;

namespace DMS.GenericRepository

{

public class GenericRepository where TEntity : class

{

internal DbSet dbSet;

public virtual void Update(TEntity entityToUpdate)

{

dbSet.Attach(entityToUpdate);

context.Entry(entityToUpdate).State = System.Data.Entity.EntityState.Modified;

}

Thanks Advance.