Errors when I click 'Wijzigingen opslaan'

I get an error when I click ‘Wijzingen opslaan’.

Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, 'eu_cookiewet_opties_validate' was given in /var/www/vhosts/steigerhoutuitfriesland.nl/httpdocs/site/wp-includes/plugin.php on line 170

Warning: Cannot modify header information - headers already sent by (output started at /var/www/vhosts/steigerhoutuitfriesland.nl/httpdocs/site/wp-includes/plugin.php:170) in /var/www/vhosts/steigerhoutuitfriesland.nl/httpdocs/site/wp-includes/pluggable.php on line 881

https://www.ads-software.com/extend/plugins/eu-cookiewet-plugin/