Yep, this is going to be a problem due to the way Headers work in general. This is not caused by BPS Pro or by anything else and is specific to NextGen Gallery. Post the php error in the NextGen Gallery plugin support forum on the wordpress.org site.
Code lines: 553-566 in file: /wp-content/plugins/nextgen-gallery/products/photocrati_nextgen/modules/nextgen_data/class.ngglegacy_gallerystorage_driver.php
// Clear output while (ob_get_level() > 0) { ob_end_clean(); } $format = strtolower($format); // output image and headers header('Content-type: image/' . $format); readfile($abspath); return true; }