most likely the groups you are creating in the access groups manager have a blank value in them
In the access groups manager, try clicking below the last text value, if you can make a selection, there is a blank value and it should be removed.
To conditionally redirect to another page based on the logged in users user level, you could add a switch case statement on the page the login redirects to. In php the code would look similar to:
<?php
switch ($_SESSION['userLevel'}) {
case 1:
header("location: VISITORSDIR/index.php";
break;
case 2:
header("location: USERSDIR/index.php";
break;
case 3:
header("location: ADMIN/index.php";
break;
}
?>