This is exactly what it is:

RewriteBase /

I tried the full domain name, with/without forward slash as well

?

Strange, did you try to comment the line completely as well?

What is your site URL? And what webserver and version are you using?

Yes, I did try to fully comment it out:

site: www.blackchinalabs.co.uk

It's a VPS running Plesk 8.6, do you think theres an additional server setting that needs to be in place?

I do know theres another Joomla account on the server that has SEF turned on (not using ArtioSEF though) from the global config, and doesn't seem to have a problem?

Ok, based on your site name, the RewriteBase should be either commented out or

RewriteBase /

So that should not be a problem.
Is the Joomla SEO in Global configuration set to Yes? (I assume so, but please confirm this).

If you are still getting the same error message, try deleting the RewriteBase line completely and write it again from scratch. Be carefull what editor are you using and what encoding is the .htaccess file stored it. Check that there are no invalid character.

This problem seems quite tricky, however I am afraid that is all I can advice.

Can you please send me an email at Diese E-Mail-Adresse ist gegen Spambots geschützt! Du musst JavaScript aktivieren, damit Du sie sehen kannst. or PM me as I'd like for you to just handle the installation and setup of the component. I spent $130 on this and addons and its useful because it can't even function. I don't mind paying for your services but I need it done today as I have client waiting on this and its taking several days when this should have been an out-of-box solution.

Ok, we will contact you. I believe we will sort this out.