At the top of the BPS Guide post you will see this:
All information below this point is older Bulletproof Security version information – everything in BPS is automated these days, but if you are looking for some manual instructions or other info - read on. After the release of BPS .46.5 a lot of this information became obsolete.
We are planning a complete website design in May or June. Currently we do not have time to do this. The guide is outdated and obsolete and really no longer necessary. Other pages are current such as the plugin compatibility checking pages and any other pages that are critical.
It is possible that the Master .htaccess file has been corrupted. It is rare but it does happen. Uninstall BPS and reinstall it and before you create a new Master secure.htaccess file, download a copy of the secure.htaccess Master file. Then continue to use AutoMagic and create a new Master .htaccess file and activate Root BulletProof Mode.
If you are still getting 500 errors then use secure.htaccess file you manually downloaded and edit it manually with your correct RewriteBase and RewriteRule and then upload it and rename it to just .htaccess. I have seen a couple of smaller hosting outfits that will corrupt the .htaccess file when you use AutoMagic - this is very rare also.
I have never heard of your web host before so maybe check with them if all the above things do not work >>> Interlink Advantage-INTERL-83. What you can do is send them a copy of the secure.htaccess file and ask them if they do not allow anything in that .htaccess file.