Error Raise when i try to implement Entity Framewor in 3Tier

Error 1 The type 'System.Data.Entity.DbContext' is defined in an assembly that is not referenced. You must add a reference to assembly 'EntityFramework, Version=4.4.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'. E:\Mukesh\R&D\19-11-2014\BOL\DataAccessClass.cs 19 13 BOL

hi guys i get the above  error  when i implement the EF in three tier in asp.

i did google and tried all the soluation but i m not able to solve it. 

please help me out...