Help with error - class 'vB_Registry' not found
 

Sorry I am new here and wasn't sure where to post this.

I keep getting this error on my forum and I am not sure how to fix it. I've posted and searched on vbulletin.org and searched google and I can't find any answers.

What does this mean:

Fatal error: Class 'vB_Registry' not found in /home/"my site"/public_html/includes/init.php on line 44