pagination problem

[eluser]E303[/eluser]
I have built a simple blog system. I have managed to get the pagination to work on the main blog posts but when I move into areas like archived posts I get a 404 error.

Code:

Controller

function archive()
{
$config['base_url'] = base_url() . 'blog/archive'.$this->uri->segment(3).'/'/$this->uri->segment(4);
#prints out http://localhost/blog/archive/february/2008/

$offset = $this->uri->segment(5);
}

[eluser]E303[/eluser]
just worked it out I was missing
index.php in front of blog/archive