Webkungen on "add_rewrite_rule not working on productiion site"

Hi

Got this in my themes functions.php file:

add_rewrite_rule(
	'activate/([a-z0-9\-]+)/?',
	'index.php?page_id=26&hash=$matches[1]',
	'top'
);

It's working in my dev site, but suddenly stopped working on the production site, I'm getting redirected to the start page. Of course I've flushed the permalinks structure.

The output from this print_r($wp_rewrite->rules);

Shows the following:
[activate/([a-z0-9\-]+)/?] => index.php?page_id=26&hash=$matches[1]

Any ideas on why it stopped working? Both dev and prod are using the same WordPress 3.8.1, only diffence between the two is that dev is running on Windows/Apache and prod. on Ubuntu/Apache.