Hello again,
after some searching on the internet, it turns out this is easy to fix:
in the file wp-contents/themes/pilot-fish/includes/widgets.php
on line 72
change
$this->WP_Widget
into
parent::__construct
so it reads:
parent::__construct('widget_pilotfish_vcard', __('pilotfish: vCard', 'pilotfish'), $widget_ops);