StartupPath not work

I set in config.ascx

aspx page:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Assembly="CKFinder" Namespace="CKFinder" TagPrefix="CKFinder" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
     <CKFinder:FileBrowser ID="FB_Gallery" BasePath="/WebSite1/ckfinder/" Width="800" runat="server"  ></CKFinder:FileBrowser>
    
    </div>
    </form>
</body>
</html>

.cs

 protected void Page_Load(object sender, EventArgs e)
    {
        FB_Gallery.StartupPath = "Images:/";
        FB_Gallery.StartupFolderExpanded = true;
 FB_Gallery.RememberLastFolder = false;
    }