Image control won't show ImageURL

I've got a black image control on my webform and a dropdownlistbox which gives a list of jpg files to choose from.  I step threw it and verify the correct path is being sent to Image1.ImageURL but no picture shows up. I can't find any other properties to set on the Image control. Also, why do I have to make pathx static? When it was private (or public) it got set to null when assigning it to target string.

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.IO;
using System.Collections;

public partial class _Default : System.Web.UI.Page 
{
    static string pathx;
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
            DirectoryInfo dInfo = new DirectoryInfo(Server.MapPath("pics"));
            pathx = dInfo.FullName;
            ArrayList alFiles = new ArrayList();
           
            alFiles.AddRange(dInfo.GetFiles("*.jpg"));

            foreach (FileInfo fInfo in alFiles)
            {
                DropDownList1.Items.Add(fInfo.Name);
            }
        }
    }
   
    protected void DropDownList1_TextChanged(object sender, EventArgs e)
    {
        string x = DropDownList1.SelectedValue;
        string target = pathx;
        target += "\\";
        target += x;
        Image1.ImageUrl = target;
    }
 
}