The fix for this issue is to edit the file listed in the error message on the server and change line 160 from:
<p><?php _e('Put a checkmark below next to the sites you would like to remove from your site list.', &$this->hook); ?></p>
to:
<p><?php _e('Put a checkmark below next to the sites you would like to remove from your site list.', array(&$this->hook)); ?></p>
Unfortunately I don’t maintain the widget so cannot update the plugin.
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