=== modified file 'og_forum.module'
--- og_forum.module	
+++ og_forum.module	
@@ -1101,6 +1101,7 @@ function og_forum_form_alter($form_id, &
         }
       }
       if (!user_access('administer forums')) {
+        unset($form['taxonomy'][$vid]['#options']['']);
         foreach ($form['taxonomy'][$vid]['#options'] as $key => $the_rest) {
           reset($the_rest->option);
           $option_key = key($the_rest->option);