Want to add dynamic url using htaccess

I want to add dynamic seo url and I think it could be done using htaccess . I have created a new page . I have added an rewrite rule i.e. RewriteRule ^newsletter-confirmation/([0-9]+)/?$ oxseo.php?cl=newsletter-confirmation&id=$1 [L,NC] in .htaccess file. But it ends to 404 error. Can anyone guide me how it can be done? In browser I am accessing this using http://host/newsletter-confirmation/173556/ where numeric value in url is dynamic. Thanks in advance.

I found a working solution. I have used

RewriteRule ^newsletter_confirm/([0-9]+)/?$ index.php?cl=newsletter_confirm&id=$1 [L,NC]
RewriteRule ^admin/?$ admin/index.php [L,NC] this in htaccess file. If I use only first line then admin login wont come so I have to write a rule for it also. But dont know the actual problem why this problem is occurring.