I enabled it, still the same error. This is my .htaccess content.
RewriteEngine on
#Some apache servers need Rewritebase.
#delete # from start of Rewrite base to enable it.
#If your forum is something like
http://www.forum-example.com/forum then modify your
#RewriteBase in this way: RewriteBase /forum
RewriteBase
RewriteCond %{QUERY_STRING} ^topic=([0-9]*).([0-9]*)
RewriteRule ^(.*)$ seo4smf-redirect.php?t=%1 [R=301,L]
RewriteCond %{QUERY_STRING} ^board=([0-9]*).([0-9]*)
RewriteRule ^(.*)$ seo4smf-redirect.php?b=%1 [R=301,L]
RewriteCond %{QUERY_STRING} ^action=profile;u=([0-9]*)
RewriteRule ^(.*)$ seo4smf-redirect.php?u=%1 [R=301,L]
RewriteCond %{QUERY_STRING} ^page=([0-9]*)
RewriteRule ^(.*)$ seo4smf-redirect.php?p=%1 [R=301,L]
#Rewrite Old urls
RewriteRule ^index.php/board,(.*).html seo4smf-redirect.php?b=$1 [R=301,L]
RewriteRule ^index.php/board,(.*).html;(.*) seo4smf-redirect.php?b=$1&o=$2 [R=301,L]
RewriteRule ^index.php/topic,(.*).html seo4smf-redirect.php?t=$1 [R=301,L]
RewriteRule ^index.php/topic,(.*).html;(.*) seo4smf-redirect.php?t=$1&o=$2 [R=301,L]
#New board URL's
RewriteRule ^(.*)-b([0-9]*).([0-9]*)/;(.*) index.php?dummy=1&board=$2.$3&$4 [L]
RewriteRule ^(.*)-b([0-9]*).([0-9]*)/ index.php?dummy=1&board=$2.$3 [L]
RewriteRule ^(.*)-b([0-9]*).([0-9]) index.php?dummy=1&board=$2.$3 [L]
#New topic URL's
RewriteRule ^(.*)-t([0-9]*).([0-9]*).html;((\?:from|msg|new)[0-9]*);(.*)$ index.php?dummy=1&topic=$2.$4&$5 [L]
RewriteRule ^(.*)-t([0-9]*).([0-9]*).html;((\?:from|msg|new)[0-9]*) index.php?dummy=1&topic=$2.$4 [L]
RewriteRule ^(.*)-t([0-9]*).([0-9]*).html;(.*)$ index.php?dummy=1&topic=$2.$3&$4 [L]
RewriteRule ^(.*)-t([0-9]*).([0-9]*).html index.php?dummy=1&topic=$2.$3 [L]
#New profiles URL's
RewriteRule ^(.*)-u([0-9]*).html;sa,(.*)$ index.php?dummy=1&action=profile;u=$2;sa=$3 [L]
RewriteRule ^(.*)-u([0-9]*).html index.php?dummy=1&action=profile;u=$2 [L]
#New Tinyportal Articles URL's
RewriteRule ^(.*)-p([0-9]*).html index.php?dummy=1&page=$2 [L]
RewriteRule sitemap.xml sitemaps.php [L]
RewriteRule urllist.txt urllist.php [L]