CMS 403 error
 

We are getting a 403 error when trying to reach our site. We are using an index redirect from our root file, to route things into our forum file in our database. We are able to reach oursite.com/forum/forum.php, but when you attempt to go to content.php which I believe is the homepage, is doesnt work and gives us the 403 error. Any reason as to why this would be happening?
thanks