CMS error when add commemt. How to fix it.
 

Code:
Fatal error: Call to undefined function modsystem_usertitle() in public_html/publishsuite/packages/vbcms/comments.php(676) : eval()'d code on line 5
Error show when i add comment to article.
Both article's created by button at Home page (content.php) and "promote to article" button at forum

My Web Hosting info
Vbulletin publishing Ver 4.0.1
PHP 5.2.9
MySQL 5.0
Apache 1.3

How to fix this bug. Ask me anymore question if you need.
Thanks for read my post.