Error when I populate a gridcontrol with entity Framework

Error when I populate a gridcontrol with entity Framework

I have a desktop application in C#. I want to populate a grid with some
lines from database(SQL Server).I want to use 3 separation layers: - 3
projects(UI,BL,DB).In DB project I used entity framework 4.4 for creating
the DB model .I wrote in designer the details for database connection and
in the model now I have all my tables with their columns and
relasionships.In this project DB ,I added a class DataSource:
public class DataSource : Component, IListSource
{
#region Declarations
private static DataSource instance;
public SalesEntities context;