No no, chmod 777 for all, only three files with chmod 755:
wbb/index.php CHMOD 755
wbb/acp/index.php CHMOD 755
wcf/acp/index.php CHMOD 755
Thats the files you are using when you using the board/wcf (in Browser). These files you can set to 755 and the 500 internal server error should not be longer displayed to oyu.