You are not authorized to view this page (403 error) in wordpress

The problem:

You receive an error message “You are not authorized to view this page. (403 error)” after inserting the username and password in the WordPress admin login page.

Solution: Enable Index.php

If your blog is hosted on a Windows server, this could be an error with Directory Indexes.

• Login to the Control Panel.
• Click on Web Options.
• Go to Directory Indexes section.
• Add index.php to the Directory Indexes.