MyBB Community Forums

When i click on a certain forum i am getting this error message now saying...

Fatal error: Call to undefined function build_prefixes() in /var/www/vhosts/wirraltalk.co.uk/httpdocs/forumdisplay.php on line 913

I am really sick and tired of getting these errors all the time can anyone help please.

reupload functions.php file from MyBB source files of your forum's version ..