Symptoms: You are running several WordPress (and/or non-WordPress) sites on a VPS installation or a single hosting account using add-on domains or subdomains. The main domain is a WordPress site which uses Admin Tools and the .htaccess Maker functionality. You are unable to access other domains except your main site.
.htaccess settings are propagated by default to the children directories. Let us give an example. Let's say that you have a main site called www.example.com and its files are inside public_html. Let's also assume that you have another subdomain called foobar.example.com whose files are stored inside public_html/foobar. What happens when you launch foobar.example.com is that Apache looks for a .htaccess in the parent directory (public_html), applies its settings, then looks for a .htaccess file inside public_html/foobar and append its settings to the ones it has already read from the previous file. It will then process the combined rules and decide what to do with the request.
Since the .htaccess file generated by .htaccess Maker forbids access to random-named directories and index.html files, access to the directories of your other domains is forbidden, thus you get a 403 error. Don't worry, there is a workaround!
First, determine the names of the directories where your other domains' files are stored. Let's say the are called "foobar" and "foobaz" so that I can provide an example. Go to your main site's back-end, Components, Admin Tools, .htaccess Maker. Expand the System Protection tab. Inside the "Allow direct access, including .php files, to these directories" text area enter the names of the directories, one directory per line. Then click on Save and Create .htaccess. This will allow you to access your other domains. Do note that at this point, your other domains -if they are Joomla!-powered- are not protected by Admin Tools' .htaccess Maker. Just install Admin Tools Professional on each one of them and use the .htaccess Maker to create .htaccess files on each one.
If this doesn't work or if it works erratically (e.g. the other
domains display as if their CSS is missing) and they are NOT built on
WordPress or anything else which uses SEF URLs / permalinks please
create a .htaccess file inside each of their directories with just the
following line inside it: RewriteEngine Off This will
work independently of whether you used the previous method, i.e.
adding exceptions for the domains' directories, as it will simply turn
off Apache's mod_rewrite engine. That engine what the secure .htaccess
generated by Admin Tools' .htaccess Maker is using to protect your
site. It will also kill off SEF URLs (they also depend on the rewrite
engine) on non-static sites, e.g. Joomla! or WordPress ones, that's
why we told you not to use it on them.