Support

As mentioned in the documentation, it's a try and error process. First, let's make sure that your server does support .htaccess files at all. Try renaming Joomla!'s htaccess.txt to .htaccess and upload it to your site (hint: it may be easier to upload it as htaccess.txt and rename it on the server). If this results to an Internal Server Error 500, please ask your host to take a look. Usually the just have to enable Apache's mod_rewrite module or point you to which features are not supported by the server.

If the stock .htaccess works, it's time to start tinkering with Admin Tools Pro .htaccess Maker. Start by disabling all features on its setup page and click on Save and Create .htaccess. This generates what is essentially a copy of Joomla!'s stock .htaccess. It shouldn't throw an error. Then, proceed by enabling one feature at a time and clicking on Save and Create .htaccess. At some point you'll hit a feature which causes an error. You'll have to leave that disabled. Proceed with the rest of them. In the end of this process you'll end up with a .htaccess which works and is optimized for your specific server.

I am glad it's working now!

Regarding the other question... You should not see it go off-line. That's the whole point. You should still see the site and everyone else, coming from a different IP, should see a static off-line page.