[D6] CKEDITOR_FORCE_SIMPLE_TOOLBAR_NAME undefined

You removed the definition of the CKEDITOR_FORCE_SIMPLE_TOOLBAR_NAME variable from the ckeditor.module file (which makes sense since the toolbar is gone.)

But you did not correct the corresponding code in the administration screen so I get errors that it is undefined.

You should be a lot more careful about those things.

  $form['ckeditor_exclude_settings']['simple_incl'] = array(
    '#type' => 'textarea',
    '#title' => t('Force simplified toolbar on the following fields'),
    '#cols' => 60,
    '#rows' => 5,
    '#default_value' => !empty($profile->settings['simple_incl']) ? $profile->settings['simple_incl'] : '',
    '#description' => t('Enter the paths to the textarea fields for which you want to force the simplified toolbar (!name).', array('!name' => CKEDITOR_FORCE_SIMPLE_TOOLBAR_NAME)) .' '. t('Please see the <a href="!helppagelink">Help page</a> for more information about defining field names. Take a look at the exclusion settings (above) for a short instruction.', array('!helppagelink' => url('admin/help/ckeditor', array('fragment' => 'fieldinclexcl')))),
    '#wysiwyg' => FALSE,
  );

And the second one:

  $form['ckeditor_exclude_settings']['simple_incl'] = array(
    '#type' => 'textarea',
    '#title' => t('Force simplified toolbar on the following fields'),
    '#cols' => 60,
    '#rows' => 5,
    '#default_value' => !empty($profile->settings['simple_incl']) ? $profile->settings['simple_incl'] : '',
    '#description' => t('Enter the paths to the textarea fields for which you want to force the simplified toolbar (!name).', array('!name' => CKEDITOR_FORCE_SIMPLE_TOOLBAR_NAME)) .' '. t('See the <a href="!helppagelink">Help page</a> for more information about defining field names. Take a look at the exclusion settings (above) for a short instruction.', array('!helppagelink' => url('admin/help/ckeditor', array('fragment' => 'fieldinclexcl')))),
    '#wysiwyg' => FALSE,
  );