500 internal server error plz help

Hi there
i upgraded my VB to version 3.7.2 and when trying to post any reply or any thread i got HTTP 500 internal server error
some one told me to updare php version to 5 and i did,but this didn't solve the problem

some people say its from htaccess rewrite code
this is my htaccess:

HTML Code:

# Comment the following line (add '#' at the beginning)
# to disable mod_rewrite functions.
# Please note: you still need to disable the hack in
# the vBSEO control panel to stop url rewrites.
RewriteEngine On
# Some servers require the Rewritebase directive to be
# enabled (remove '#' at the beginning to activate)
# Please note: when enabled, you must include the path
# to your root vB folder (i.e. RewriteBase /vb)
#RewriteBase /
RewriteCond %{HTTP_HOST} !^www\.mysite\.net
#RewriteRule (.*) http://www.mysite.net/vb/$1 [L,R=301]
RewriteRule (.*) http://www.mysite.net/vb/ [L,R=301]
RewriteRule ^((urllist|sitemap_).*\.(xml|txt)(\.gz)?)$ vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]
RewriteCond %{QUERY_STRING} !vbseourl=
RewriteCond %{REQUEST_URI} !(admincp/|modcp/|chat|cron)
RewriteRule ^(.*\.php)$ vbseo.php?vbseourl=$1 [L,QSA]
RewriteCond %{REQUEST_FILENAME} !\.(jpg|gif)$
RewriteRule ^(archive/.*)$ vbseo.php?vbseourl=$1 [L,QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !^(admincp|modcp|clientscript|cpstyles|images)/
RewriteRule ^(.+)$ vbseo.php?vbseourl=$1 [L,QSA]
RewriteEngine On
RewriteRule ^((urllist|sitemap).*\.(xml|txt)(\.gz)?)$ vbseo_sitemap/vbseo_getsitemap.php?sitemap=$1 [L]
ExpiresActive On 
ExpiresByType image/gif "access 1 week" 
ExpiresByType image/jpg "access 1 week" 
ExpiresByType image/jpeg "access 1 week" 
ExpiresByType image/png "access 1 week" 
ExpiresByType text/css "access 1 week" 
ExpiresByType text/js "access 1 week" 
ExpiresByType application/x-shockwave-flash "access 1 week" 
ExpiresByType application/x-javascript  "access 1 week"  
EnableSendfile Off

plz let me know if any one can solve this problem for me
waiting your help

[How to] Check if mod_rewrite is working for my site

Does it work if you replace your current htaccess with the default vBSEO htaccess?

This bit looks a bit odd.

RewriteCond %{HTTP_HOST} !^www\.mysite\.net
#RewriteRule (.*) http://www.mysite.net/vb/$1 [L,R=301]

As in, why not just use the currently hashed-out one? It looks to be the correct one, with the $1 at the end.

hi there
i solved the problem it was from xml file
but is there any wrong in my htaccess?
thanx every one!