I installed JoomSEF, and I prepared and uploaded the htaccess file as per documentation. I checked the Rewritebase in the hosting provider's support section to confirm that it should be uncommented with only a slash for installation in my account's public root (but when I got errors also tried putting in the path).
I checked that sef is turned on in the global configuration panel. I also saved the JoomSEF configuration with JoomSEF 'on'.
To try and eliminate possible causes of errors I disabled mXcomment (which needs a JoomSEF plugin that I did not install yet) and I uncommented the optional third party line in the manual's htaccess text that was the only one still commented.
My hosting provider is Siteground where countless other Joomla sites are placed, no doubt many with JoomSEF.
So, as far as I can see I did everything according to the book, but as soon as I put the htaccess file in place I get 403 errors saying that access is forbidden - both in the admin backend and on all pages in the frontend.
What else is there that I can do? Any suggestions would be greatly appreciated!
UPDATE: Commenting out the line \"Options FollowSym_link_s\" made it all work.