How to delete images from temp folder i save images in MembershipUserId_abc.jpg format

Question

How to delete  images from temp folder i save images in MembershipUserId_abc.jpg format   delete event is happen when user is logout i can global.asax  please help me

global.asax.cs
      
           protected void Session_End(object sender, EventArgs e) {

string uId = Membership.GetUser(Context.User.Identity.Name).ProviderUserKey.ToString();  //here i got an error Object reference not set to an instance of an object.

string path;

string[] filename;

path = System.Web.HttpContext.Current.Server.MapPath("~/temp/");

filename = Directory.GetFiles(path);

for (int i = 0; i < filename.Length; i++) {

       if (Session.SessionID == Path.GetFileName(filename[i])) {

               string imgpath = filename[i];

               FileInfo filepath = new FileInfo(imgpath);

               if (filepath.Exists) {

filepath.Delete();

               //  Session.Abandon();

         

               }

       }

}

}