[eluser]Aken[/eluser]
1) RewriteCond conditions expire after the first RewriteRule. So you must repeat conditions for each RewriteRule if you have some that are the same.
2) You have a regular expression syntax error in your admin rewrite.
3) From this .htaccess file, it looks like you're using query strings instead of the slash-separated URL structure that CI defaults with? I've replaced it with what a standard CI .htaccess file would typically use. You should revert back if that was initially correct.
4) I can't say if this will solve all your problems. I've never used more than one CI application on a single instance, and don't know what else is required to set it up properly. But this will at least fix what's incorrect in the .htaccess file.
Code:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
#Removes access to the system folder by users.
#Additionally this will allow you to create a System.php controller,
#previously this would not have been possible.
#'system' can be replaced if you have renamed your system folder.
RewriteCond %{REQUEST_URI} ^system.*
RewriteRule ^(.*)$ /main.php/$1 [L]
#When your application folder isn't in the system folder
#This snippet prevents user access to the application folder
#Submitted by: Fabdrol
#Rename 'application' to your applications folder name.
RewriteCond %{REQUEST_URI} ^application.*
RewriteRule ^(.*)$ /main.php/$1 [L]
#Checks to see if the user is attempting to access a valid file,
#such as an image or css document, if this isn't true it sends the
#request to main.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUE/ST_FILENAME} !-d
RewriteRule ^(.*)$ /main.php/$1 [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^admin/(.*)$ /admin.php/$1 [L]
</IfModule>
<IfModule !mod_rewrite.c>
# If we don't have mod_rewrite installed, all 404's
# can be sent to main.php, and everything works as normal.
# Submitted by: ElliotHaughin
ErrorDocument 404 /main.php
</IfModule>