message i'm getting on one of our sites

site url: http://bccinlandempire.com/
I turned on debug mode and got the following message when I visit the site:

Notice: Constant NGG_PLUGIN already defined in /home/bnmnewpr/public_html/bccinlandempire/wp-content/plugins/nextgen-gallery/nggallery.php on line 580 Warning: Cannot modify header information - headers already sent by (output started at /home/bnmnewpr/public_html/bccinlandempire/wp-content/plugins/nextgen-gallery/nggallery.php:580) in /home/bnmnewpr/public_html/bccinlandempire/wp-includes/pluggable.php on line 1207