I should imagine some local/environmental issue to be honest.

Do not forget that there is no such thing as logging into Simple:Press.  The login process is controlled and carried out by WordPress. Simple:Press simply passes the name and password values across to WordPress. WordPress, as the site management system, carries out the validation etc.

Do you oerhaos have a conflict with another login or perhaps membership plugin? That might explain it.

I don’t use any plugin for login, i use the standard wordpress login.

As Andy has already explained it definitely sounds like a local issue, do you have the same problem logging in to WP?

No, if i go in the default login page the page load without probelm.

Personally I would ask your host why it behaves differently. They should be able to explain the 403.

I don’t think that the problem is with the host because the second time it works.

If i try to access, the first time gives me 403, if i load the login page and go back (even without login) does work.

i am unsure what you mean by the login page… although I assume you mean the standard WP form.

But I was suggesting you go and talk to your host in case they can explain the 403 by looking in the logs. At this point in time you are the only user reporting any such problem so it is something in your environment that is the cause. Your host may well be in a position to supply the answer.

Solved

The problem was in .htaccess, i’ve added this code and now it’s ok

RewriteEngine On

RewriteCond %{REQUEST_URI} ^/

RewriteRule .* – [CO=wordpress_test_cookie:WP+Cookie+check:%{HTTP_HOST}:1440:/]

Thanks for the support

Curious. Not encountered that one before!
Good news though and thanks for the update and information.