Contraint Violation When Reading From Database

I have created a typed-dataset AuthorsDataSet and created a table in with name Authors, manually by right-click > New > Table. I have kept the data-types, sizes and contstriants exactly same as the table in the database, though I have kept the Column names different. I am filling the AuthorsDataSet with the following code on Form_Loadif (!IsPostBack)

{      SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["pubsConnectionString"].ConnectionString);

      SqlCommand cmd = new SqlCommand("SELECT au_id, au_lname, au_fname, phone, address, city, state, zip, contract FROM authors", conn);      using (SqlDataAdapter da = new SqlDataAdapter(cmd))

      {

            conn.Open();

            da.Fill(ds.Authors);

            grdAuthors.DataSource = ds.Authors;

            grdAuthors.DataBind();

            conn.Close();

      }

      conn.Dispose();

      cmd.Dispose();

}

The connection string is as follows:<connectionStrings>

      <add name="pubsConnectionString" connectionString="Data Source = localhost; Initial Catalog = pubs; Integrated Security = SSPI"/>

</connectionStrings>

The following error occurs when I run the page

System.Data.ConstraintException: Failed to enable constraints. One or more rows contain values violating non-null, unique, or foreign-key constraints.