Autoselection textbox not displaying the result from db

HI,

I have created an autoselection textbox in awebform like this
  <asp:ScriptManager ID="ScriptManager1" runat="server" />
                <asp:TextBox ID="txtSearch" runat="server" ></asp:TextBox>
                <asp:AutoCompleteExtender ID="AutoCompleteExtender1" runat="server" TargetControlID="txtSearch" ServicePath="~/WebService1.asmx" ServiceMethod="GetCountryInfo" MinimumPrefixLength="1" >
                </asp:AutoCompleteExtender>

And a webservice as follows which returns the country list from db

public string[] GetCountryInfo(string prefixText)
{
 //int count = 10;
 string sql = "Select * from tblCountry Where CountryName like @prefixText";
 string connectionString = System.Configuration.ConfigurationManager.ConnectionStrings["TestDatabaseConnectionString"].ToString();
 SqlDataAdapter da = new SqlDataAdapter(sql,connectionString);
 da.SelectCommand.Parameters.Add("@prefixText", SqlDbType.VarChar, 50).Value = prefixText+ "%";
 DataTable dt = new DataTable();
 da.Fill(dt);
 string[] items = new string[dt.Rows.Count];
 int i = 0;
 foreach (DataRow dr in dt.Rows)
 {
  items.SetValue(dr["CountryName"].ToString(),i);
  i++;
 }
 return items;
}

When i type a letter in the textbox, the control is going to service method and it returns the result correctly ,but my problem is the result is not showing as a list in the textbox.Still the textbox is showing only the typed letter not the result from service method.

Can anybody pls help me in this
Thanks in advance
Nisha