Here's my error, running 4.1.7 with no vBSEO:
Code:
[13-Dec-2011 09:58:58] PHP Fatal error: require_once() [<a href='function.require'>function.require</a>]: Failed opening required '/home/xxxx/public_html/forums./includes/functions_user.php' (include_path='xxxxx') in /home/xxxx/public_html/forums/forumdisplay.php(1063) : eval()'d code on line 2
The problem is the "." after the "forums" in the required path. It's like your script is assuming only a relative path but something in vB is asserting and absolute path first.