Invoking Button

[Tddupre]

here is my form code for the button i need to invoke

<tr><td colspan="2" align="right">
<input type="hidden" name="subjoin" value="1">
<input type="submit" value="Join!"></td></tr> 

this is part of my process.php which process the data given it, this determines the user is doing

function Process(){
      global $session;
      /* User submitted login form */
      if(isset($_POST['sublogin'])){
         $this->procLogin();
      }
      /* User submitted registration form */
      else if(isset($_POST['subjoin'])){
         $this->procRegister();
      }
      /* User submitted forgot password form */
      else if(isset($_POST['subforgot'])){
         $this->procForgotPass();
      }
      /* User submitted edit account form */
      else if(isset($_POST['subedit'])){
         $this->procEditAccount();
      }
      /**
       * The only other reason user should be directed here
       * is if he wants to logout, which means user is
       * logged in currently.
       */
      else if($session->logged_in){
         $this->procLogout();
      }
      /**
       * Should not get here, which means user is viewing this page
       * by mistake and therefore is redirected.
       */
       else{
          header("Location: index.php");
       }
   } 

Here is the VB.net code

 WebBrowser1.Document.GetElementById("Join!").InvokeMember("click")

It doesn't invoke the button, should be an easy fix