Forum how can I start troubleshoot, what cause this error
 

My website : http://www.petsfanatics.com/forum/forum.php show below error

Warning: fetch_template() calls should be replaced by the vB_Template class. Template name: forumhome_loggedinuser in [path]/includes/functions.php on line 3957

Parse error: syntax error, unexpected T_STRING in /home1/tiptopwe/public_html/web-petsfanatics.com/forum/forum.php(647) : eval()'d code(61) : eval()'d code on line 1

how can I start troubleshoot, what cause this error? Thanks