getting error in retrieving data from database using jquery/json

[WebMethod]
public static maj_hd[] bind_repter(String maj_hd)
{
     List<maj_hd> list = new List<maj_hd>();
     DataTable dt = new DataTable(); 
     using (SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["constringBA"].ConnectionString))
     {
          SqlCommand cmd = new SqlCommand("sql query", con);
          using (cmd) 
          {
              con.Open();
              SqlDataAdapter da = new SqlDataAdapter(cmd);
              da.Fill(dt);
          }
     }
     return list.ToArray();
}