Full HTML Formatter / WYSIWYG Not Working In Views 3?
I believe it's a lazy-load editor problem. The WYSIWYG libraries aren't being loaded on the parent page, so they are not available to the modal window. If you're using the WYSIWYG module with CKEditor, something like this should alleviate your issue.

&lt;?php
  // Views support.
  if (module_exists('views') &amp;&amp; $form_id == 'views_ui_edi') {
    // Load potential editor.
    foreach (filter_formats() as $format =&gt; $object) {
      if ($profile = wysiwyg_get_profile($format)) {
        wysiwyg_load_editor($profile);
        wysiwyg_add_plugin_settings($profile);
        wysiwyg_add_editor_settings($profile, 'advanced');
      }
    }
  }
?&gt;


from http://drupal.org/node/356480#comment-1190907

and the patch located in - 

http://drupal.org/node/356480#comment-4256204