In your htaccess file, find the line remove the update keyword
RewriteCond %{QUERY_STRING} ^.*(md5|benchmark|union|select|insert|cast|declare|drop|update|alter).* [NC]
change it to
RewriteCond %{QUERY_STRING} ^.*(md5|benchmark|union|select|insert|cast|declare|drop|alter).* [NC]
SMF uses update in the url which is an SQL keyword.