For the last 8 days, I've been unable to access my WordPress installations through Lunarpages (I have four, set up on subdomains). Whenever I try, I get a screen that says "Not Acceptable"; this happens with all browsers.
I've written Lunarpages tech support, but they asked me to provide them with temporary login credentials. Um, guys - if I could do that, I wouldn't need you.
While I don't know the WP software itself, it seems an access issue [to the WP itself--not that it's denying you.]
I would check the config file that comes with WP and check that it's all configured properly.
My second guess would be to venture into your site/cpanel and access Phpmyadmin. Look inside the database for general configuration errors. My hunch is that your cookies is possibly done incorrectly, or that each site uses the same cookie.
Just my 2 cents.