lucy24 - 7:43 pm on Sep 24, 2013 (gmt 0)
Keep all RewriteRules in the primary htaccess. mod_rewrite behaves a little differently from other Apache mods, so you have to treat it with caution.
Before anything else: Does your existing htaccess have other RewriteRules that do work as intended? If you don't know, make up a nonsense rule like
RewriteRule foobar http://www.example.com/widget.html [R=301,L]
and make sure it works. (Look at browser's address bar, not at page content.)
Does the forum use a CMS that uses rewriting? If so, you need to find those rules and make sure your additions go in the right places and don't conflict with existing rules.