vBSEO is causing redirect loops

I have a problem in my vBulletin-forum because vBSEO is causing redirect loops in Firefox. The error message that firefox users see when they open certain URLs rewritten by vBSEO is:

Redirect Loop

Redirection limit for this URL exceeded. Unable to load the requested page. This may be caused by cookies that are blocked.

The browser has stopped trying to retrieve the requested item. The site is redirecting the request in a way that will never complete.

This is the default Firefox error message that appears when Firefox has stopped an endless loop after redirecting a request to the same URL 20 times.

The strange thing is that I have copied my forum-database and all php-files to a different server and everything is working fine there. That means, the reason for this problem is not my vBSEO-config, my vBulletin-forum or any vBulletin-addons (because there's no redirect loop on the different server).
Either vBSEO is not compatible with my current server configuration and software or the problem is somewhere in my server configuration (but outside of the vbulletin-folder).
My current configuration is: Linux Debian Lenny, PHP 5.2.6, FastCGI, Apache 2.2.9.

I was able to find at least one place in my forum that is causing these problems and I will describe it now. Maybe that helps to find the reason for these redirect loops:

If I am trying to open an URL that was created by vBSEO and where the "virtual subfolder" does not exist in the filesystem as a real folder, the following happens. I'm trying to open the URL
http://forum.mydomain.tld/tags (without trailing slash!)
and I am not being redirected to the URL containing the trailing slash that would look like this:
http://forum.mydomain.tld/tags/

But if I'm trying to open a subfolder that really exists in the filesystem and where the link has not been created and handled by vbseo, Apache is appending the trailing slash automatically. So for example, http://forum.mydomain.tld/images is being redirected to http://forum.mydomain.tld/images/ automatically.
That means that there is a different behaviour when opening "URLs without trailing slash" regarding the fact that Apache is handling them or vBSEO is handling them.

And now comes the very strange thing: I have told you that I have copied the whole forum to a different server to test it there. And on this server vBSEO does append a trailing slash to all URLs (whereas it does not do it on my server).

And the connection to my "redirect loop"-problem is, that the redirect loop always happens if people are trying to open these URLs "without trailing slash". But the error message only appears in Firefox. But I am not the only one who sees this error, because all Firefox-users in my forum are seing these errors too and there's a large thread in my forum where people are complaining about it! I have attached a screenshot of the firebug-extension in my firefox browser where you can see the error message and below the timeline of the whole redirect loop after calling the URL http://forum.mydomain.tld/groups
The error message is german in this screenshot because I have installed the german firefox, but you can read the english version of this error message quoted at the beginning of this thread.

My question is now: why does vBSEO produce this redirect loop on my server instead of simply appending a slash to the URLs (like it does on the other server where I have tested it and like on all other servers where vBSEO is currently running)?

VERY IMPORTANT: PLEASE READ THE FOLLOWING CAREFULLY!
Before you are trying to reproduce this error on my webserver and forum: I have currently suppressed most of the errors by adding the following line to my .htaccess file:

Code:

RewriteRule ^(([^/]+/)*[^./]+)$ http://forum.mydomain.tld/$1/ [L,R=301]

This htaccess-rule appends the trailing slash to all "non slash"-URLs. I have added this line in my .htaccess-file before vbseo.php is called and the redirect loop errors have become less (but they didn' t disappear completely).

But I can remove this line from my .htaccess-file again if the vBSEO-support-team wants to try to reproduce these errors using Firefox (the only browser where you can see those errors). My vBSEO-ticket-ID for this problem is 8913-QOPC-6517. I was talking german in this ticket so far but it seemed like there was a problem with the language barrier. To the vBSEO-support-team: you can reply in this support ticket in english from now on.

If anyone should have an idea what could be the reason for vBSEO's behaviour on my server regarding the trailing slashes, please let me know. P.S.: mod_rewite is working fine for all other domains that are running on the same server. The problem only exists with vBSEO.

As i already responded your ticket , this issue can't be produced on any other board then yours. Therefor you need to supply us login details so we can examine this detailed.

I don't have FTP installed on my dedicated server (because it is not secure enough). I am doing everything using SSH. But if I'm trying to create a new SSH-account for you and to limit it to certain folders, this does not work. You are always able to see all files on the whole server. And I don't want to give external companies like vBSEO full access to all private data on this server, including all user emails etc.
Please tell me which files you would like to see and I will post them into the ticket. What do you need? httpd.conf? Virtualhost-Config? Anything else?

We need the following informations :

A working ftp or ssh login for your forum folder
Admincp Login information
vBSEO Control Panel information
and details for your httpd.conf and virtual_hosting configuration.

For your information i have the exact same setting ( Linux Debian Lenny, PHP 5.2.6, FastCGI, Apache 2.2.9. ) within my server and the issues you explain can't be reproduced on my own server.

I have attached the apache2.conf and virtualhost-config to the support ticket. If I should find a way to limit a SSH-account to the forum folder, I will let you know.

And by the way: you already have the vBSEO control panel login information. I have added it 3 times(!!) to the ticket since 1 week by using the link "Modify Question Properties" (although you and your other support-members are still continuing to ask for it)!
I have also added the username and password for the admincp to the ticket (in the last reply to the ticket because your "Modify Question Properties"-form does not seem to work properly).

Hi Andy,

You are quite right there is an issue with that part of the ticket system at the moment and in a similar manner we are in contact with Deskpro about that issue, I can see you have now supplied the details as a reply and I do thank you for that.

I do need to assure you that we have no intention of searching your files , folders or e-mails . We are requesting ftp or ssh access to help you identify the issue as quick as possible. Up to today lots of users supplied us login details and all these details are kept private and our Support Staff are professional not to browse your other files expect identifying the problem.

Don't get me wrong I can fully understand your concerns it is only sensible business to want to protect your details but I can assure you we are only asking for you these details so we can correctly debug and test on your installation.

I have installed an AJAX-based webftp-client and I have created a new user account for you pointing to the forum-directory. You can find the login-details in the support-ticket.

But whatever you will do in my forum folder or vBSEO-CP: please remember that all of these files are running perfectly on a different server where I have copied all forum files and the database one by one without changing a single byte in any file (see first post in this thread). That means, that it is not a general misconfiguration of vBSEO in my vbulletin-Forum-folder because these files are running perfectly on other servers. It only seems to be an incompatibility with my general server configuration and/or software.