Basically everything fails when moving online

[eluser]Varzock[/eluser]
Hi all, newbie here *waves*

So, I have built my first CI application (gotta say I'm falling in love with this). Everything works fine when I'm working on it locally, but as soon as I make it online (uploading to a host dir), it starts falling apart... sigh.

I have quite a simple login system that checks user and pass in database and if they're correct, redirects the user to main page. Now when I login succesfully, the site goes to an infinite redirect loop. I have checked there are no loops in my models that would cause the infinite redirecting and I can't figure out what's causing it.

Let's say the site can be found at addy xxxyyyzzz.com/admin

My default route:
$route['default_controller'] = "login";

Index page:
$config['index_page'] = "";

My .htaccess file is as follows:

Code:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /xxxyyyzzz/index.php?/$1 [QSA,L]
</IfModule>

<IfModule !mod_rewrite.c>
    # If we don't have mod_rewrite installed, all 404's
    # can be sent to index.php, and everything works as normal.
    # Submitted by: ElliotHaughin

    ErrorDocument 404 /index.php
</IfModule>

And:
$config['base_url'] = "http://www.xxxyyyzzz.com/admin/";

I have tried to search and read threads here that would help me on my way but no luck so far Any help/hint is greatly appreciated. I am soon about to jump out of the window

[EDIT: Forgot to mention I moved my app from Windows to Linux]

[EDIT: I'm terribly sorry, I just noticed I posted this in the wrong section. Any admin there, could you please move this to a correct place? Thanks ]