Server Error in '/' Application. The resource cannot be found. How to fix it?

Server Error in '/' Application.
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The resource cannot be found. 
Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable.  Please review the following URL and make sure that it is spelled correctly. 

Requested URL: /Admin/~Admin/AddNewProducts.aspx


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Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.18408 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using ShoppingProject.BusinessLayer;
 
namespace ShoppingProject.Admin
{
    public partial class AddNewProducts : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                GetCategories();
 
                AddSubmitEvent();
 
                if (Request.QueryString["alert"] == "success")
                {
                    Response.Write("<script>alert('Record Saved Successfully.');</script>");
                }
            }
 
        }
 
        private void AddSubmitEvent()
        {
            UpdatePanel updatePanel = Page.Master.FindControl("AdminUpdatePanel") as UpdatePanel;
            UpdatePanelControlTrigger trigger = new PostBackTrigger();
            trigger.ControlID = btnSubmit.UniqueID;
 
            updatePanel.Triggers.Add(trigger);
        }
 
        private void GetCategories()
        {
            ShoppingCart k = new ShoppingCart();
            DataTable dt = k.GetCategories();
            if (dt.Rows.Count > 0)
            {
                ddlCategory.DataValueField = "CategoryID";
                ddlCategory.DataTextField = "CategoryName";
                ddlCategory.DataSource = dt;
                ddlCategory.DataBind();
            }
        }
 
        protected void btnSubmit_Click(object sender, EventArgs e)
        {
            if (uploadProductPhoto.PostedFile != null)
            {
                SaveProductPhoto();
 
                ShoppingCart k = new ShoppingCart()
                {
                    ProductName = txtProductName.Text,
                    ProductPrice = txtProductPrice.Text,
                    ProductImage = "~/ProductImages/" + uploadProductPhoto.FileName,
                    ProductDescription = txtProductDescription.Text,
                    CategoryID = Convert.ToInt32(ddlCategory.SelectedValue),
                    TotalProducts = Convert.ToInt32(txtProductQuantity.Text)
                };
                k.AddNewProduct();
                // Alert.Show("Record Seved Successfully");
                ClearText();
                Response.Redirect("~Admin/AddNewProducts.aspx?alert=success");
 
            }
            else
            {
                //Alert.Show("Upload Product Photo");
                Response.Write("<script>alert('Please UpLoad Photo');</script>");
            }
 
        }
 
        private void ClearText()
        {
            uploadProductPhoto = null;
            txtProductName.Text = string.Empty;
            txtProductPrice.Text = string.Empty;
            txtProductDescription.Text = string.Empty;
            txtProductQuantity.Text = string.Empty;
        }
 
        private void SaveProductPhoto()
        {
            if (uploadProductPhoto.PostedFile != null)
            {
                string filename = uploadProductPhoto.PostedFile.FileName.ToString();
                string fileExt = System.IO.Path.GetExtension(uploadProductPhoto.FileName);
 
                //check file name length
                if (filename.Length > 96)
                {
                    //Alert.Show("image name should not exceed 96 character !");
                }
                //check filetype
                else if (fileExt != ".jpeg" && fileExt != ".jpg" && fileExt != ".png" && fileExt != ".bmp")
                {
                    //Alert.Show("Only jpeg,jpg,bmp & png imags are allowed!");
                }
 
                //check file size
                else if (uploadProductPhoto.PostedFile.ContentLength > 4000000)
                {
                    //Alert.Show("image size should not be greater than 4MB !");
                }
                //Save images into Images folder
                else
                {
                    uploadProductPhoto.SaveAs(Server.MapPath("~/ProductImages/" + filename));
                }
 
            }
        }
    }
}