[RESOLVED] Session Problem

[Visual Basic.Net]

I wrote this to secure the page by password & username:

@session_start();
if($_POST['mkses']){
	$_SESSION['id']=$_POST['id'];
	$_SESSION['pass']=$_POST['pass'];
}
if($_SESSION['id']!="aaa" and $_SESSION['pass']!="aaa"){
	echo '<form method="post" action='.$_SERVER[PHP_SELF].' >';
	echo "<input type='text' name='id'><input type='text' name='password'>";
	echo "<input type='submit' name='mkses' value='login'></form>";
	exit;
}

when I enter the password & username it display page without problem, the page consists of a form to enter information and the form Action is set to the same page, when I click submit it show me the message to enter username and password again, that means it didn't save the session?

what is the problem?
thank's