Server Error in '/bramandam site' Application.

The control with ID 'AutoCompleteExtender1' requires a ScriptManager on the page. The ScriptManager must appear before any controls that need it.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.  Exception Details: System.InvalidOperationException: The control with ID 'AutoCompleteExtender1' requires a ScriptManager on the page. The ScriptManager must appear before any controls that need it. Source Error: 

Stack Trace: 

[InvalidOperationException: The control with ID 'AutoCompleteExtender1' requires a ScriptManager on the page. The ScriptManager must appear before any controls that need it.]
   System.Web.UI.ExtenderControl.get_ScriptManager() +327169
   System.Web.UI.ExtenderControl.RegisterWithScriptManager() +117
   System.Web.UI.ExtenderControl.OnPreRender(EventArgs e) +19
   AjaxControlToolkit.ExtenderControlBase.OnPreRender(EventArgs e) in f:\TeamCity\buildAgent\work\80acd78aa4c25314\Server\AjaxControlToolkit\ExtenderBase\ExtenderControlBase.cs:365
   AjaxControlToolkit.AutoCompleteExtender.OnPreRender(EventArgs e) in f:\TeamCity\buildAgent\work\80acd78aa4c25314\Server\AjaxControlToolkit\AutoComplete\AutoCompleteExtender.cs:375
   System.Web.UI.Control.PreRenderRecursiveInternal() +80
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Control.PreRenderRecursiveInternal() +171
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +842

Version Information: Microsoft .NET Framework Version:2.0.50727.4984; ASP.NET Version:2.0.50727.4971

my code 

 public static List<string> GetCountries(string prefixText)
    {
        SqlConnection con = new SqlConnection(ConfigurationManager.AppSettings["s"].ToString());
        con.Open();
        SqlCommand cmd = new SqlCommand("select * from bramandam where Name like @Name+'%'", con);
        cmd.Parameters.AddWithValue("@Name", prefixText);
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable dt = new DataTable();
        da.Fill(dt);
        List<string> CountryNames = new List<string>();
        for (int i = 0; i < dt.Rows.Count; i++)
        {
            CountryNames.Add(dt.Rows[i][1].ToString());
        }
        return CountryNames;
    }