Access is denied due to invalid credenti

[sqlbabe]

Script URL: http://www.elitefokker.be/guestbook/gbook.php
Version of script:
Hosting company:
URL of phpinfo.php:
URL of session_test.php:
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My guestbook has worked fine untill now. Suddenly I get the following error.
401 - Unauthorized: Access is denied due to invalid credentials

I did not make any changes in the last 2 or 3 months, and I already tried to CHMOD the files, but that did not resolve the issue either.

I don't really understand what credentials could be wrong and other pages in this folder can be accessed without a problem.

What am I missing and how can I resolve this issue?

[Klemen]

This is not an error GBook generates, but your server.

Something is wrong on the server-side. You will need to talk to your hosting company (or webmaster?) why the server is sending a 401 error.