配置文件：

<?xml version="1.0" encoding="utf-8" ?> <configuration>

  <connectionStrings>

    <add name="Strcon" connectionString="Data Sourse=.\SQLEXPRESS;Initial Catalog=Province_City;Integrated Security=True"/>

</connectionStrings>

</configuration>

DAL中sqlhelpe的：

 public static readonly string Strcon =
            ConfigurationManager.ConnectionStrings["Strcon"].ConnectionString;

 public static DataTable ExecuteDataTable(string cmdText,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(Strcon))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = cmdText;            
                    cmd.Parameters.AddRange(parameters);
                    using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
                    {
                        DataTable dt = new DataTable();
                        adapter.Fill(dt);
                        return dt;
                    }
                }
            }
        }

DAL中类的

 class Province_City
    {
        public static DataTable Getdata()
        {
            string sql = "select * from Province_City where ParentID=@id";
            object i=0;
            return sqlhelper.ExecuteDataTable(sql,new SqlParameter("id",i));
        }
    }

出现的问题是：

DAL.sqlhelper”的类型初始值设定项引发异常。

是怎么回事？请教高手