Attempting to register when captcha is enabled produces:

Warning: Cannot modify header information - headers already sent by (output started at /var/www/qi/boards/a111/cache/ctpl_subsilver2_overall_header.html.php:2) in /var/www/qi/boards/a111/includes/functions.php on line 2486

General Error
template locator: File ./styles/subsilver2/template/

{CAPTCHA_TEMPLATE} does not exist

Looks like the new template engine does not support <!-- INCLUDE {CAPTCHA_TEMPLATE}

--> syntax.