i think i see the probelm, in connMiradaDropdown2.php
$choice2 = mysql_real_escape_string($_GET['choice']);
$query = "SELECT * FROM categories WHERE Category='$choice' ORDER BY CategoryShort ASC";
should be:
$choice2 = mysql_real_escape_string($_GET['choice']);
$query = "SELECT * FROM categories WHERE Category='$choice2' ORDER BY CategoryShort ASC";
basically, in the first line you are creating the $choice2 variable, but you currently have the query set to use a variable named $choice, which does not exist, it is named $choice2