Default user messages at admin/settings/better404 are missing </p>:
<p>Sorry, but the page you were trying to get to, !url, doest not exists.<p><p>...

Maybe add to module ie:

/**
 * Implementation of hook_init().
 */
function better404_init() {
  global $conf;
  $conf['i18n_variables'][] = 'better404_case1_message';
  $conf['i18n_variables'][] = 'better404_case2_message';
  $conf['i18n_variables'][] = 'better404_case3_message';
  $conf['i18n_variables'][] = 'better404_case4_message';
}