The url I am using for each site was created by Securitycheck Pro. I thought that meant I was using backend protection. Like I said, they have been working OK previously. I have this note saved for my own reference concerning the site that is not working.:
"url is result of Protection feature of Securitycheck extension
Last edit: 8 months 3 days ago by Jose. Reason: Avoid secret key disclosure
If the .htaccess fie doesn't contain the "backend protection" and any other reference to Securitycheck Pro then it is not applied. Can you send me administrative credentials to access to cpanel (or ftp) and to Joomla backend? If so use the email from which you receive forum notifications.