Going on a hunch that your problem is with register_globals, try adding this code to the top of your php file:
Code:
/* Assign variables if register_globals = OFF */
$StartMonth = $_POST['StartMonth'];
$StartDay = $_POST['StartDay'];
$StartYear = $_POST['StartYear'];
$EndMonth = $_POST['EndMonth'];
$EndDay = $_POST['EndDay'];
$EndYear = $_POST['EndYear'];
$report_type = $_POST['report_type'];
This will assign all the variables from the _POST array. Let me know if this works.