Lots of forums topics say about a function on Contact For 7 plugin that crashes the upload on NextGEN Gallery.
Fatal Error: Call to undefined function wpcf7_add_tag_generator() in /public_html/wp-content/plugins/contact-form-7/modules/text.php on line 152
On this link an user show the workaround with this, that is the change of a line on a NGG file from:
require_once( WP_LOAD_PATH . 'wp-load.php');
require_once( WP_LOAD_PATH . 'wp-admin/admin.php');
I hope that you can update the plugin so that we won't need this change on next versions.