Undefined Widget only on Homepage

Hello still have the problem with undefined, but not only in the header, though only on the homepage and only at one plugin.

the name of the plugin is: gd products center:

Here is my debug note, can it have something to do with one of that issues:

Warning: Call-time pass-by-reference has been deprecated; If you would like to pass it by reference, modify the declaration of gdpc_property_value(). If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file in /srv/www/vhosts/reisezielvergleich.de/httpdocs/wp-content/plugins/gd-products-center/code/core/render.php on line 96 Notice: wp_register_script was called incorrectly. Scripts and styles should not be registered or enqueued until the wp_enqueue_scripts, admin_enqueue_scripts, or init hooks. Please see Debugging in WordPress for more information. (This message was added in version 3.3.) in /srv/www/vhosts/reisezielvergleich.de/httpdocs/wp-includes/functions.php on line 2944 Notice: add_custom_background ist seit Version 3.4 veraltet! Benutze stattdessen add_theme_support( ‘custom-background’, $args ). in /srv/www/vhosts/reisezielvergleich.de/httpdocs/wp-includes/functions.php on line 2824 Notice: Constant WP_MEMORY_LIMIT already defined in /srv/www/vhosts/reisezielvergleich.de/httpdocs/wp-config.php on line 100 Notice: get_theme_data ist seit Version 3.4 veraltet! Benutze stattdessen wp_get_theme(). in /srv/www/vhosts/reisezielvergleich.de/httpdocs/wp-includes/functions.php on line 2824 Notice: get_settings ist seit Version 2.1 veraltet! Benutze stattdessen get_option(). in /srv/www/vhosts/reisezielvergleich.de/httpdocs/wp-includes/functions.php on line 2824