Same problem, but i’ve got it works now.
step 1 : copy “your-full-width-page.php”. mine is template-fullwidth.php (if you not sure this is a full width page, open the file with editor like dreamweaver, wordpad, etc and make sure it has no “side bar” layer).
step 2 : rename the “your-full-width-page.php” to “forum.php” and put it to \your-site-name\wp-content\themes\your-theme
step 3 : then open the “forum.php” you just copy with editor (and rename all class of the <div>)
example <div id=”primary” class=”content-area”> to <div id=”primary2″ class=”content-area2“>
step 4 : simply refresh the browser and BAM!
