Wrong implementation of form_set_error

In custom_breadcrumbs.admin.inc at line 123 you have

form_set_error(t('Every link path must have a matching title. There are !paths paths, and !titles titles.', array('!paths' => $path_count, '!titles' => $title_count)));

but the definition in D6 is form_set_error($name = NULL, $message = '', $reset = FALSE), so your the code should look something like:

form_set_error('titles', t('Every link path must have a matching title. There are !paths paths, and !titles titles.', array('!paths' => $path_count, '!titles' => $title_count)));