Hello.

I have a server with VBulletin forum (working under Apache 2.2, CentOS). The default settings for it in .htaccess are as follows:

RewriteEngine on

RewriteCond %{HTTP_HOST} ^gsmforum\.ru
RewriteRule (.*) http://www.gsmforum.ru/$1 [R=301,L] 

# If you are having problems or are using VirtualDocumentRoot, uncomment this line and set it to your vBulletin directory.
RewriteBase /

RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d

RewriteRule ^.*$ - [NC,L]

# Forum
RewriteRule ^threads/.* showthread.php [QSA]
RewriteRule ^forums/.* forumdisplay.php [QSA]
RewriteRule ^members/.* member.php [QSA]
RewriteRule ^blogs/.* blog.php [QSA]
ReWriteRule ^entries/.* entry.php [QSA]

RewriteCond %{REQUEST_FILENAME} -s [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d

RewriteRule ^.*$ - [NC,L]

# MVC
RewriteRule ^(?:(.*?)(?:/|$))(.*|$)$ $1.php?r=$2 [QSA]

If I try to access any non-existent URL on forum like www.example.com/ajdsjaskasajs, server throws HTTP 500 error.

Apache log says:

[Sun Apr 25 17:24:32 2010] [error] [client 82.211.152.12] Request exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace., referer: http://www.gsmforum.ru/forumdisplay.php?424-%CD%EE%E2%EE%F1%F2%E8-%EF%F0%EE%E3%F0%E0%EC%EC%E0%F2%EE%F0%EE%E2

If I switch LogLevel to Debug I get something like this:

[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php.php.php.php.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php.php.php.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php.php.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt.php
[Sun Apr 25 17:30:46 2010] [debug] core.c(3059): [client 95.25.70.85] redirected from r->uri = /robots.txt
[root@server2 logs]# tail httpd_error.log
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php.php.php.php.php.php.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php.php.php.php.php.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php.php.php.php.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php.php.php.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php.php.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript.php, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru
[Sun Apr 25 17:31:27 2010] [debug] core.c(3059): [client 217.118.79.27] redirected from r->uri = /clientscript/vbulletin_css/style-d95b06dc-00001.css, referer: http://74.125.77.132/search?q=cache:bGPJ8XkSvlMJ:www.gsmforum.ru/showthread.php%3Ft%3D62479+%D0%A3%D0%BC%D0%B5%D0%BD%D1%8C%D1%88%D0%B5%D0%BD%D0%B8%D0%B5+%D0%BF%D0%B8%D0%BD%D0%B3%D0%B0+3G+%D0%BC%D0%BE%D0%B4%D0%B5%D0%BC&cd=3&hl=ru&ct=clnk&gl=ru

If I remove or comment the last (#MVC) line from .htaccess all is fine. Can you advise me what is the problem with mod_rewrite settings?

Why does the last line cause infinite recursion?