Reemplaza todo por esto:
Código PHP:
Options -MultiViews +FollowSymlinks -Indexes
#
# If mod_security is enabled, attempt to disable it.
# - Note, this will work on the majority of hosts but on
# MediaTemple, it is known to cause random Internal Server
# errors. For MediaTemple, please remove the block below
#
<IfModule mod_security.c>
# Turn off mod_security filtering.
SecFilterEngine Off
# The below probably isn't needed, but better safe than sorry.
SecFilterScanPOST Off
</IfModule>
#
# 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
DirectoryIndex portal.php
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]
<IfModule mod_env.c>
SetEnv SEO_SUPPORT 1
</IfModule>
</IfModule>
#
# If Apache is compiled with built in mod_deflade/GZIP support
# then GZIP Javascript, CSS, HTML and XML so they're sent to
# the client faster.
#
<IfModule mod_deflate.c>
AddOutputFilterByType DEFLATE application/javascript text/css text/html text/xml
</IfModule>
fue por instalar plugins al cerrar sesion igual se dejaba en blanco se soluciono