Request Entity Too Large when forcing logging

Hi, I hope somebody here can help me. I’m trying to restrict access to the site to only people that are registered.

I tried nearly all plugins available that does that but they all fail at the same place.

Once I restrict the access, the default site url http://www.mysite.org to access the site give me the error 413
Request Entity Too Large
The requested resource
/wp-login.php
does not allow request data with GET requests, or the amount of data provided in the request exceeds the capacity limit.

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

http://mysite.org/wp-login.php?redirect_to=http%3A%2F%2Fmysite.org%2F

I’m clueless. There is probably something wrong set on the server.

Any idea?