error mess.

I get this message, what is wrong, can you update the plugin?

Notice: Use of undefined constant wwp_plugin_directory_name – assumed ‘wwp_plugin_directory_name’ in /customers/f/b/7/xxx.dk/httpd.www/butik/wp-content/plugins/woo-wholesale-pricing/inc/class-woo-wholesale-functions.php on line 13 Warning: Cannot modify header information – headers already sent by (output started at /customers/f/b/7/xxx.dk/httpd.www/butik/wp-content/plugins/woo-wholesale-pricing/inc/class-woo-wholesale-functions.php:13) in /customers/f/b/7/xxx.dk/httpd.www/butik/wp-admin/includes/misc.php on line 1114