Better WP Security adds a tweaks in your .htaccess causing the problem with SI Captcha
In your. Htaccess Find this line
RewriteCond %{QUERY_STRING} ^.*(bash|git|hg|log|svn|swp|cvs) [NC,OR]
and then put him
#RewriteCond %{QUERY_STRING} ^.*(bash|git|hg|log|svn|swp|cvs) [NC,OR]
see if it works, work for me