کد HTML:
RewriteOptions inherit
#

# MyBB "search engine friendly" URL rewrites

# - Note, for these to work with MyBB please make sure you have

#   the setting enabled in the Admin CP and you have this file

#   named .htaccess

#

<IfModule mod_rewrite.c>

    RewriteEngine on

    RewriteRule ^forum-([0-9]+).html forumdisplay.php?fid=$1 [L,QSA]

    RewriteRule ^forum-([0-9]+)-page-([0-9]+).html forumdisplay.php?fid=$1&page=$2 [L,QSA]

    RewriteRule ^thread-([0-9]+).html showthread.php?tid=$1 [L,QSA]

    RewriteRule ^thread-([0-9]+)-page-([0-9]+).html showthread.php?tid=$1&page=$2 [L,QSA]

    RewriteRule ^thread-([0-9]+)-lastpost.html showthread.php?tid=$1&action=lastpost [L,QSA]

    RewriteRule ^thread-([0-9]+)-nextnewest.html showthread.php?tid=$1&action=nextnewest [L,QSA]

    RewriteRule ^thread-([0-9]+)-nextoldest.html showthread.php?tid=$1&action=nextoldest [L,QSA]

    RewriteRule ^thread-([0-9]+)-newpost.html showthread.php?tid=$1&action=newpost [L,QSA]

    RewriteRule ^thread-([0-9]+)-post-([0-9]+).html showthread.php?tid=$1&pid=$2 [L,QSA]

    RewriteRule ^post-([0-9]+).html showthread.php?pid=$1 [L,QSA]

    RewriteRule ^announcement-([0-9]+).html announcements.php?aid=$1 [L,QSA]

    RewriteRule ^user-([0-9]+).html member.php?action=profile&uid=$1 [L,QSA]

    RewriteRule ^calendar-([0-9]+).html calendar.php?calendar=$1 [L,QSA]

    RewriteRule ^calendar-([0-9]+)-year-([0-9]+).html calendar.php?action=yearview&calendar=$1&year=$2 [L,QSA]

    RewriteRule ^calendar-([0-9]+)-year-([0-9]+)-month-([0-9]+).html calendar.php?calendar=$1&year=$2&month=$3 [L,QSA]

    RewriteRule ^calendar-([0-9]+)-year-([0-9]+)-month-([0-9]+)-day-([0-9]+).html calendar.php?action=dayview&calendar=$1&year=$2&month=$3&day=$4 [L,QSA]

    RewriteRule ^calendar-([0-9]+)-week-(n?[0-9]+).html calendar.php?action=weekview&calendar=$1&week=$2 [L,QSA]

    RewriteRule ^event-([0-9]+).html calendar.php?action=event&eid=$1 [L,QSA] 
<Files 403.shtml>
order allow,deny
allow from all
</Files>
این برای انجمن ساز MyBB هستش...
بعد تو فایل error_log رو که چک میکنم این ارور 403.shtml همیشه هست توش