HTACCESS file doesent work in sub-folder

[eluser]yNaxon[/eluser]
hello,
I am using the htaccess code that was given in codeigniter's user guide:

Code:

RewriteEngine on
RewriteCond $1 !^(index\.php|images|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]

it only works if the installation is located in the root directory. if it's located in a sub-folder, it doesen't work.

any idea how to make it work also under sub-category?

thanks