403/404 Error on Editing Posts after upgrading to 2.5

I’ve upgraded to 2.5 using the plugin Automatic Upgrade and everything I try to edit a post it gives me

Forbidden

You don’t have permission to access /news/wp-admin/post.php on this server.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I’ve already re-uploaded all files manually and I’m using the same htacess as the one I used on a site where the upgrade went fine.

I’ve also tried cleaning up the cookies and loging on Internet Explorer (I use FireFox)

Any ideas?