My b2evolution Version: 4.0.4

Hi guys.

I'm getting an error when i try to comment on a post.
This is the message:

Forbidden

You don't have permission to access /blog/htsrv/comment_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 checked the files permissions into that folder and all is set to 644. Even with 755 it doesn't work.

Any ideas?