sql connection error

OP stated that he has already checked that ... an hour ago

namespace BusinessLayer
{
public class EmployeeBusinessLayer
{
public IEnumerable Employees
{
get
{
string connectionString = ConfigurationManager.ConnectionStrings["DBCS"].ConnectionString;
List employees = new List();
using (SqlConnection con = new SqlConnection(connectionString))
{
SqlCommand cmd = new SqlCommand("AllEmployees", con);
cmd.CommandType = CommandType.StoredProcedure;
con.Open();
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
Employee employee = new Employee();
employee.EmployeeID = Convert.ToInt32(dr["EmployeeID"]);
employee.Name = dr["Name"].ToString();
employee.Gender = dr["Gender"].ToString();
employees.Add(employee);

}
}
return employees;

}
}
}

connection string :
<connectionstrings>
<add name="DBCS"
="" connectionstring="Server=.;Database=project; Integrated Security=SSPI;" providername="System.Data.SqlClient">

connectionString="Server=.;Database=databasename; Integrated Security=SSPI;"


this is the connection string i have also changed this using uderid password and data source