how to clear error timer

i have designing in my web page. i have use timer control in asp.net .the error are occur how to clear error how to run the timer

My code

 public partial class _Default : Sys开发者_运维知识库tem.Web.UI.Page 
  {
    protected void Page_Load(object sender, EventArgs e)
    {

    }
  }

 public interface IScheduledItem

{

void AddEventsInInterval(DateTime Begin,
         DateTime End, ArrayList List);

    DateTime NextRunTime(DateTime time);
}

the error he type or namespace name 'ArrayList' could not be found

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Add a reference to System.Collections to your project, and a using statement for System.Collections.

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You need to reference the correct namespace like this:

using System.Collections.ArrayList;

Add this to the top of you file.