[Plugin: Like-Button-Plugin-For-WordPress] conflict with 'get_category_parents' function

With the plugin activated (that’s the ONLY thing I changed), I get this error message on a ‘single’ post:

Catchable fatal error: Object of class WP_Error could not be converted to string in …edited…out…/functions/breadcrumbs.php on line 32

The conflicting function: http://codex.wordpress.org/Function_Reference/get_category_parents

This is the ‘line 32’:
echo '<li> » '. get_category_parents( $category_id, TRUE, " » " );
If I change it to this, with the Plugin activated, it displays ‘Home > 1’ but at least the ‘single’ post doesn’t break:
echo '<li> » '. 1/* get_category_parents( $category_id, TRUE, " » " ) */;

http://wordpress.org/extend/plugins/like-button-plugin-for-wordpress/