how to know which button is clicked in mvc

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ASP.NET

MVC4

entity-framework

I have a View with 2 panels which is SignIn and SignUp .In signIn Panel i have Login button and Clear button ,In signUp Panel I have SignUp and Clear Button.
I got this error when i try to login with wrong password.

Model.

public ActionResult Index()
        {

            var list = new SelectList(new[]
{
    new { ID = "1", Name = "MySelf" },
    new { ID = "2", Name = "My Son" },
    new { ID = "3", Name = "My Daughter" },
    new{ ID="4" ,Name="My Brother"},
     new { ID = "5", Name = "My Sister" },
      new { ID = "6", Name = "My Relative" },
      new { ID = "6", Name = "My Friend" },
},
"ID", "Name",1);


            ViewBag.profileList = list;

            ViewBag.ReligionList = new SelectList(db.Religion, "ReligionId", "ReligionName");

            ViewBag.languageList = new SelectList(db.Languages, "LanguageId", "LanguageName");
            ViewBag.StateList = new SelectList(db.States, "stateId", "Statename");
            return View();
        }
 [HttpPost]
        public ActionResult Index(MemberLogin memberlogin)
        {
           

                if (ModelState.IsValid)
                {

                    bool value = db.MemberLogins.Any(o => o.EmailAddress == memberlogin.EmailAddress &&
                        o.Password == memberlogin.Password);

                    if (value)
                    {
                        return RedirectToAction("Index", "MemberHome");
                    }
                    else
                    {
                        return View();
                    }
                }
               
           

            return View();
        }

My question is

1) [HttpPost] method get fires when i click any button in my View, How do i know which button is Clicked?if i clicked signin button i got to move Home page if clear clicked i got to clear all controls.

2) I got this error

There is no ViewData item of type 'IEnumerable<SelectListItem>' that has the key 'profileList'

when i click SignIn Button or SignUp button but the ProfileList Loaded completely before i Click any button.
How do i solve this?