Apache Errors on Article save

Hi,

every time I save a post, I get an apache error written: [error] PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, cannot access private method wp_piwik::onPostStatusTransition() in /vda3/var/www/httpdocs/wp-includes/plugin.php on line 470, referer: http://www.xy.com/wp-admin/post.php?post=916&action=edit

Can you tell me, what´s going on?

I use a WordPress Multisite and Piwik 2.3.0. Do you need any further information?

best,

Ben

https://ww.wp.xz.cn/plugins/wp-piwik/