Mike, could you run a quick test running the sitemapxml after editing /includes/classes/bmz_image_handler_class.php, finding this section at the top:
Code:
if (!defined('IH_DEBUG_ADMIN')) {
    define('IH_DEBUG_ADMIN', 'false');
}
if (!defined('IH_DEBUG_STOREFRONT')) {
    define('IH_DEBUG_STOREFRONT', 'false');
}

if (!defined('IS_ADMIN_FLAG')) {
    exit('Illegal access');
}
and changing the IH_DEBUG_STOREFRONT setting to 'true'? Once you've run the sitemap, change that back to 'false' again.

You should find one (or more) /logs/ih_debug*.log files. You can either post the contents back here or, if they're too big or have 'sensitive' information, send me those directly.