I see the argument "wwwRedirect" in my forum URL.

When you set up your forum, you specified that the site URL was www.yoursite.com. However, when you try to access your site, you are using just the domain "yoursite.com".

SMF is, correctly, because of the settings, automatically redirecting you to the www URL of your site address.

You can do several things 1- access the site using the www. 2- change your site settings to remove the www from your site URL and all URLs of themes, smilies, attachments, etc. (use repair_settings.php) 3- use an htaccess redirect to automatically (and invisibly) redirect users to the version of your URL that you want to use.