OK I understand what's going on - but the second screen is where you set up the comparison, so should it not be:
userName = <?php echo((isset($_POST["username"]))?$_POST["username"]:""); ?>
userPassword = <?php echo((isset($_POST["userpassword"]))?$_POST["userpassword"]:""); ?>
to compare those two columns with their correponding form values. I thought I had defined the unique column to be the email address so that if a user registers using an email address that has already been used will be sent to the login page as they are already registered, so perhaps I had misinformed you. Now when I log in I'm taken to the users_Profile page. Everything appears to be working correctly now. Thanks!